Process For The Production Of Colored Coatings

Abstract

A process for the production of colored surfaces on zinc, tin and lead-tin coatings by the provision of oxide films having light interference effects; zinc, tin and lead-tin alloys for use in the process; and alloy coating compositions and colored articles produced thereby. A molten alloy of zinc, tin or lead-tin with a minor amount of an oxygen-avid element such as titanium, manganese or vanadium is oxidized by exposure to a free oxygen-containing gas under controlled time and temperature conditions for the provision of a surface film of an oxide of the oxygen-avid addition element having light interference color characteristics.

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application, Ser. No. 574,684, filed Aug. 24, 1966 now U.S. Pat. No. 3,530,013.

Description

BACKGROUND OF THE INVENTION

This invention relates to a process for the production of colored surfaces and is particularly directed to a process for the production of colored zinc, tin and lead-tin coatings and to alloy coating compositions therefor.

The phenomenon of colored metal surfaces produced by oxidation of a metal is known as, for example, in the tempering of steels to increase toughness, the degree of tempering being characterized by specific surface colors. The tempering process, and attendant color which is a measure of the degree of tempering, can be arrested as desired by quenching.

The formation on ferrous bodies of an oxide film having a thickness characterized by a color ranging from light yellow to purple and gray for subsequent reconversion to the parent metal by reduction is taught in Sendzimir U.S. Pat. No. 2,197,622.

It is also known to color metal surfaces, particularly iron or nickel, by forming a layer of less than 2 microns thickness on the surface of the metal by electrodepositing lead oxide thereon, as is taught in British Pat. No. 1,010,065.

And, it is known to oxidize articles of titanium and titanium alloys containing more than 20 percent titanium by anodic treatment of said articles in an aqueous electrolyte to impart surface coloring and improved corrosion resistance thereto, as described in British Pat. No. 1,046,929. Commercial anodizing processes necessitate costly surface preparation to provide a substrate which is receptive to an oxide film and which will provide maximum reflectivity.

It is not known, however, how to color surfaces in a predictable and facile manner by the use of molten zinc alloyed with an oxygen-avid addition agent whereby the zinc functions as a carrier of the addition agent for the formation of a film of an oxide of said addition agent having light interference properties. Such colored coatings are not formed under normal galvanizing conditions.

SUMMARY OF THE INVENTION

We have found that the addition of a minor amount of certain oxygen-avid addition agents to zinc, tin or lead-tin and oxidation of the resulting alloys surprisingly results in the production of surface films of oxides of the addition agents, substantially free of host metals, having light interference color characteristics to produce coatings or surfaces having attractive and predictable surface colors and textures. More particularly, we have discovered a novel process for the production of colored zinc surfaces and of colored zinc coatings on articles comprising, in general, the steps of forming an alloy of zinc and an oxygen-avid element selected from the group consisting of titanium, manganese, vanadium, columbium, zirconium, thorium and mischmetal, applying the alloy composition to a surface or to a surface of the article such as by dipping said article in a melt of the alloy or flowing the molten alloy onto the article surface, and contacting the resulting molten coating with a free-oxygen-containing gas under controlled time and temperature conditions to permit reaction of the molten alloy composition with oxygen for the provision of a thin oxide film having desirable light interference color characteristics and effects.

We have also discovered that the alloying of cadmium, arsenic, copper, lead or chromium with zinc and oxidation of the resulting alloy at elevated temperatures of at least about 625.degree. C. results in the production of colored coatings when applied to surfaces.

It is a principal object of the present invention, therefore, to provide a process for the production of colored zinc, tin and lead-tin alloy coatings.

It is another object of the present invention to provide colored coatings on the surfaces of workpieces in a manner adaptable for use with galvanizing techniques, with optimum control and consistency of color.

It is another object of the present invention to provide a process for the production of colored metal oxide coatings using zinc as an inexpensive and convenient carrier of the metal from which the color is derived.

It is another object of the invention to provide highly reflective inner surfaces for colored coatings on workpieces in a manner that obviates the need for elaborate polishing of the article being coated.

DESCRIPTION OF THE DRAWINGS

Additional objects and the manner in which they can be attained will become readily apparent to one skilled in the art from the following detailed description of the invention, reference being had to the following drawings, in which:

FIG. 1 is a graph illustrating the effect of bath temperature and composition on yellow color formation for a Zn--Mn alloy;

FIG. 2 is a graph illustrating the effect of bath temperature and cooling rate on variable color formation for a Zn--Mn alloy;

FIG. 3 is a graph illustrating the effect of bath temperature and cooling rate on variable color formation for a Zn--Ti alloy; and

FIG. 4 is a graph illustrating the effect of bath temperature and cooling rate on variable color formation for a Zn--V alloy.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the process of the present invention and with particular reference now to zinc coatings, colored coatings can be produced on surfaces of various metals such as iron, steel, copper, nickel, zinc and other metals, and on surfaces of nonmetallic materials such as graphite by applying to said surfaces a coating of zinc having alloyed therewith an oxygen-avid addition agent such as manganese, titanium and vanadium in amount sufficient to form on the coating, upon reaction of the surface of said coating with oxygen, an oxide film derived from the addition agent, said film having light interference colors. Any material which is amenable to receiving a coating of the zinc alloy, under suitable temperature conditions and other operating conditions discussed hereinbelow, can be color coated according to the process of the invention.

The colors formed on the surfaces of zinc coatings containing alloying elements are due to light interference effects that are dependent on the thickness of thin oxide films. Transmission of a portion of an incident beam and subsequent reflection from the inner surface of the film can result in the reinforcement of one color and the interference with and dimming of other colors in the part of the incident beam that is reflected at the outer surface.

The characteristics of the interference colors are dependent on the index of refraction and absorbing power of the film, as well as on the reflectivity of the surfaces. Hence, differing color shades and intensities and to some extent, different color sequences, result from interference effects on films of different materials.

It will be understood that the term "oxygen-avid element (or addition agent)" refers to an element that forms a stable oxide film of suitable thickness for the production of light interference color effects. Elements such as sodium and potassium that will not form stable oxide films, and aluminum and magnesium that will not form a film of suitable thickness, do not provide light interference color effects and are not included in this term for the operation of the process of the invention.

Table 1 records observations of sequences of colors that were obtained by progressively increasing the thickness of the oxide film on a zinc titanium alloy bath, which is generally representative of the color sequence obtained with the various alloys of the invention. Beyond the fourth order, the coloring effects decrease and disappear. --------------------------------------------------------------------------- TABLE

I First Order yellow (gold) red blue silver Second Order yellow red blue green Third Order yellow red green Fourth Order yellow (narrow range) red green Fifth Order red __________________________________________________________________________

The films are believed to consist of oxides of the alloying metals which appear to react preferentially with oxygen. The thin films, generally having a thickness within the range of from about 120 A. to about 3,100 A., are formed in layers with an increasing oxygen to metal ratio towards the surface of the film. For example, in the case of titanium alloyed with zinc, we have found that the film on the coating is substantially zinc-free and consists of an oxide or oxides of titanium with rutile (TiO.sub.2) formed on the surface (or anatase [TiO.sub.2 ] with a layer of rutile below the anatase) and a layer of Ti.sub.2 O.sub.3 below the rutile. Adjacent to the Ti.sub.2 O.sub.3 is zinc-titanium alloy depleted of titanium in accordance with the amount of oxide formed. In an extreme case, it is conceivable that the metal in contact with the Ti.sub.2 O.sub.3 would be zinc substantially completely depleted of titanium. With a steel substrate, the coating is bonded to the steel by transition layers of zinc-iron alloys.

Similarly, films formed on zinc-manganese coatings have been found to be substantially free of zinc and are believed to consist of oxides of manganese with MnO.sub.2 at the surface, and Mn.sub.2 O.sub.3, Mn.sub.3 O.sub.4, and MnO between the MnO.sub.2 and the zinc-manganese alloy (or zinc, if the manganese has been completely depleted). With a steel substrate, there are transition layers of zinc-iron alloys.

The films formed on zinc-vanadium coatings also are substantially free of zinc, and the oxide film is believed to consist of V.sub.2 O.sub.5 at the surface, underlain by V.sub.2 O.sub.4, V.sub.2 O.sub.3, VO, depleted zinc base alloy (or zinc) and, with a steel substrate, transition layers of zinc-iron alloys.

In FIGS. 2-4, color sequences, which can be obtained reproducibly, are shown for manganese, titanium and vanadium alloyed with zinc. The different alloying elements produce differing color shades and intensities, e.g., soft pastel shades from the titanium alloy system and more intense colors from the vanadium system. Color brilliance, a quality of the process, is believed to be due to the smooth interface between the film and the zinc alloy, a protected reflecting surface being formed as the molten alloy solidifies.

The zinc alloy coating can be applied to surfaces of substrates by spraying the alloy in molten form onto said surfaces, by pouring molten alloy said surfaces, or by immersing or dipping said surfaces into a bath of the molten alloy. The thus-coated surfaces are contacted with a free oxygen-containing gas such as air, with or without further heating, and then cooled to form a solid coating with a thin oxide film derived from the addition agent and producing the desired color. The thickness of the oxide film, and hence the final color, is dependent upon the alloy composition, alloy temperature, and the period of time the coating, at an elevated temperature, is permitted to react with oxygen.

Although the description will not principally proceed with particular reference to binary alloys of zinc with manganese, titanium, or vanadium, it will be understood that the invention is intended to include binary, ternary, quaternary and the like alloys of the said addition agents with zinc as well as the above-mentioned addition agents of the group consisting of columbium, zirconium, thorium and mischmetal, and the group consisting of cadmium, arsenic, copper, lead and chromium.

With reference now to FIG. 1, the effect of bath or initial coating temperature and composition of zinc-manganese baths is shown relative to time of contact with the oxygen in air for the occurrences of first, second and third orders of the color yellow on the melt surface, the manganese content of the zinc bath being controlled at levels of 0.04 percent, 0.07 percent, 0.11 percent and 0.33 percent by weight. It will be evident from the graph that the occurrence of first order yellow at manganese concentration of 0.11 percent and 0.33 percent was almost instantaneous at all temperature above about 419.degree. C., i.e., the melting point of the alloy. At manganese concentrations of 0.07 percent and below, however, considerable time was necessary for the occurrence of first order yellow even at bath temperatures up to about 480.degree. C. and 500.degree. C.; the occurrence of first order yellow for a 0.04 percent manganese content occurring only at a temperature above 520.degree. C. after 50 seconds of exposure to oxygen. Thus, a range of manganese contents above 0.07 percent by weight in the zinc is desirable, the practical lower limit being about 0.1 percent concentration above which increases in the manganese content do not appreciably increase the rate of color formation. The upper practical limit is determined by the solubility of the manganese in the zinc at the operating temperatures since manganese in excess of its solubility would be present in elemental or intermetallic compound form. Excessive amounts of manganese may be added to compensate for additive losses through bath oxidation or the like losses. The presence of manganese exceeding the solubility limit will not prevent the formation of colored coatings.

Comparable tests conducted on zinc-vanadium alloy baths established the occurrence of the first order yellow at a bath temperature of 500.degree. C. at 8 seconds for a 0.018 percent by weight vanadium content, 15 seconds for a 0.011 percent by weight vanadium content, and 19 seconds for a 0.009 percent by weight vanadium content. The first order yellow appeared at 3 seconds at vanadium concentrations in the zinc of 0.076 percent and 0.46 percent by weight at an alloy bath temperature of 500.degree. C. The color occurrence was therefore relatively consistent at vanadium contents by weight in the zinc at and above about 0.075 percent, the practical lower limit being about 0.1 percent by weight. The upper practical limit is determined by the solubility of vanadium in zinc at the operating temperatures, amounts of vanadium in excess of the solubility limit and present in elemental or intermetallic compound form not preventing the formation of colored coatings.

Tests conducted on zinc-titanium alloy baths established the occurrence of first order yellow at a temperature of 500.degree. C. at 7 seconds for titanium contents in the zinc of 0.09 percent and 0.16 percent by weight. Color occurrence was relatively consistent at titanium concentrations down to 0.008 percent by weight, and at concentrations below 0.008 percent by weight the rate of coloration decreased rapidly. The lower practical limit is 0.1 percent by weight titanium in zinc and the upper practical limit is determined by the solubility of titanium in zinc at the operating temperatures. Amounts of titanium in excess of the solubility limit and present in elemental or intermetallic compound form do not prevent the formation of colored coatings.

The foregoing alloy composition ranges and limits of manganese, vanadium and titanium with zinc were established by color occurrence on the respective alloy bath surfaces. Color occurrences were noted for each alloy composition at concentrations as low as 0.0001 percent by weight. Color occurrences on dipped articles were noted at manganese, vanadium and titanium concentrations by weight in zinc of 0.02 percent, 0.001 percent and 0.001 percent respectively at alloy bath temperatures of 600.degree. C., 650.degree. C. and 650.degree. C. respectively, as will be evident from the following example. It will be understood that although the preferred and practical composition ranges and limits were determined by color formation on bath surfaces, the parameters apply equally to dipped articles, only the time of color formation being changed because of the effect of cooling of the article by exposure to air. Prolonged retention of dipped articles at elevated temperatures in a free-oxygen-containing environment such as air can be controlled to approximate bath temperature conditions and hence rate and extent of color formation can also be controlled.

The preferred lower limit for manganese, vanadium and titanium of 0.1 percent by weight in the zinc permits compensation for loss of the alloying element in the bath. The upper practical limit for alloys of manganese, vanadium and titanium with zinc can be determined by their respective solubility limits at the operating temperatures or by their respective eutectic compositions if it is desired to avoid precipitation of the addition agents from the solutions upon temperature variations of the bath. The eutectic compositions for the above alloys of manganese and titanium with zinc, about 0.45 percent Mn or about 0.45 percent Ti, were obtained from pages 1,243 and 964 respectively of "The Constitution of Binary Alloys," Second Edition 1958, M. Hansen, McGraw-Hill Book Company, Ltd. The eutectic composition for the alloys of vanadium with zinc, about 0.15 percent V, was obtained from Transactions of the Metallurgical Society of AIME, Vol. 227, page 485, 1953. The preferred range for the alloy compositions of manganese, vanadium and titanium with zinc to avoid precipitation is therefore from about 0.1 percent by weight to about the eutectic composition of the respective alloying element in zinc, that is, from about 0.1 percent to about 0.45 percent for manganese and titanium, and from 0.1 percent to about 0.15 percent for vanadium.

The following example, results of which are shown in table II, describes concentration effects at lower composition levels on color occurrences on dipped samples coated with compositions of manganese, titanium and vanadium alloyed with zinc. Tests were conducted in which specimens of galvanized sheet steel of three thicknesses, 30-, 24- and 16-gauge, were dipped in baths of zinc-manganese alloy within the temperature range of 500.degree. C. to 600.degree. C. and zinc-titanium and zinc-vanadium alloys within the temperature range of 500.degree. C. to 650.degree. C. All specimens were allowed to reach the bath temperature before withdrawal for exposure to ambient air conditions for coating solidification.

Initial tests were conducted wherein the bath temperatures were maintained constant and the alloying agents were diluted until no coloration was observed on dipped samples. The bath temperatures were then raised in steps, maintaining the alloy composition, until color was again produced on the dipped samples. This procedure of diluting the alloying agents to first eliminate color and then raising the bath temperature to produce color at the same alloy composition was continued until no coloration on dipped samples occurred at the established upper temperature limits. Assay samples were taken for each dilution step and, together with color observations, were tabulated as shown in table II. The first three zinc-manganese bath compositions represent calculated values and the remaining compositions in table II represent wet analysis results. ##SPC1##

The following example illustrates the effect of regulating the length of effective time of reaction of oxygen with the zinc alloy. A series of 16-, 24- and 30-gauge pregalvanized panels and one-half inch diameter rods were dipped into melts of zinc containing 0.1 percent manganese, zinc containing 0.15 percent titanium and zinc containing 0.15 percent vanadium. The panel immersion time and bath temperature were varied and the freezing time of the coating and final color were noted. At each temperature level, the melt surface was skimmed and color formation was also timed. Results plotted on the graphs in FIGS. 2, 3 and 4 show the effect of cooling rate and bath temperature on the formation of colors on the surface of dipped articles. With reference to the graphs, the areas bounded by fine solid lines are the colors observed on the surface of the melt, representing a zero-cooling rate, and the areas bounded by heavy solid lines are the final colors that are formed on the surface of dipped articles, both upon exposure to air. The areas defined by both groups of solid lines indicate the actual colors observed. The broken lines represent the coating freezing times for 30-, 24- and 16-gauge sheet specimens, air cooled at room temperature of 20.degree. C. and the heavy solid-lined areas intersected indicate the final colors that form on the specimen surfaces when dipped at particular temperatures.

The observations tabulated in table III may be made from the graphs of FIGS. 2-4; in each case immersion times being sufficient for the specimens to attain bath temperature and the coatings subsequently air cooled at room temperature (20.degree. C.). --------------------------------------------------------------------------- TABLE III

Bath Bath Final Analysis Temperature Material Coating Figure (by weight) (.degree.C.) Gauge Color __________________________________________________________________________ 2 Zn-0.1% Mn 475 24 yellow 2 Zn-0.1% Mn 475 16 blue 3 Zn-0.15% Ti 500 30 yellow 3 Zn-0.15% Ti 500 16 red 4 Zn-0.15% V 500 30 red 4 Zn-0.15% V 500 16 blue __________________________________________________________________________

The foregoing examples relate to colors achieved where the dipped article was allowed to air cool from the bath temperature. By quenching the article with cold air blasts, a color appearing earlier in the color sequence is formed. Immersion times insufficient to attain the bath temperature also form colors appearing earlier in the sequence. By decreasing the cooling rate or increasing bath temperature, a color appearing later in the color sequence can be formed, as for example, where an article is dipped, held at the bath temperature (zero-cooling rate) for a prolonged time, and then rapidly cooled by quenching when the desired color had formed. If desired, the article can also be heated after dipping, and subsequently cooled or quenched, or a finished article can be reheated for further color change by means of, for example, induction heating.

The graphs indicate that the effect of cooling rate on color formation is more pronounced on the zinc-manganese (Zn-0.1 percent Mn) alloy than on either the zinc-titanium (Zn-0.15 percent Ti) or zinc-vanadium (Zn-0.15 percent V) alloys.

Immersion times when dipping articles in molten baths are not critical when coating nonreactive materials, provided, of course, that a suitable temperature is reached for the desired color if no post heating is provided. However, with a reactive substrate such as low alloy steel or the usual mild steel sheet used in conventional galvanizing operations, and particularly for continuous operation an immersion time of less than 1 minute is preferred. We have found immersion times of from about one up to about 20 seconds satisfactory for the application of a uniform layer of the zinc alloy, provided the coating is post heated after short immersions to ensure uniform thickness and adequate oxidation of the coating surface for formation of the oxide film of desired thickness and resulting color. Post heating can be accomplished by means of, for example, induction heating.

The foregoing Sendzimir patent, illustrative of the disclosures of the prior art, teaches that the presence of from 0.001 percent to 0.35 percent aluminum in zinc is necessary for effective bath control in the continuous galvanizing of metal surfaces with zinc. In general, small additions of aluminum in amount of about 0.003 percent normally are made to zinc baths for control of surface dross in the galvanizing of structural shapes and fabricated articles. We have found that the presence of about 0.002 percent to about 0.005 percent by weight aluminum in the zinc alloy bath precludes formation of a desirable oxide film having light interference effects. The presence of as little as 0.0005 percent by weight aluminum, while not sufficient to prevent coloration, does decrease the rate of color formation sufficiently to impede the operation of the process of the present invention.

Although it will be understood the invention is free from hypothetical considerations, it is believed that the presence of the aluminum in amounts of 0.005 percent and more results in the aluminum preferentially oxidizing to form a protective film of Al.sub.2 O.sub.3 which prevents the formation of, for example, TiO.sub.2, V.sub.2 O.sub.5 or MnO.sub.2 oxide films. In that the Al.sub.2 O.sub.3 layer is extremely thin, no light interference colors are obtained.

The following example, conducted to establish deleterious aluminum concentrations, describes tests conducted in which the aluminum content of zinc alloy baths was increased from 0 to 0.005 percent by weight.

Melts of commercial Special High Grade zinc (99.99+ percent) with titanium (Zn-0.15 percent Ti), manganese (Zn-0.15 percent Mn) and vanadium (Zn-0.15 percent V) were held at a constant temperature, and aluminum, in the form of a zinc aluminum alloy (Zn-1.0 percent al. was added to each melt to increase the concentration of aluminum by increments by weight of 0.0005 percent. The rate of color formation on the surface of the melt and the color formed on the dipped panel were noted after each addition of aluminum. The results are listed in table IV. ##SPC2##

The foregoing tests were made with commercial Special High Grade zinc. Other commercial grades of zinc, e.g., Prime Western which contains up to 1.5 percent Pb, can be used provided that the foregoing limitations regarding aluminum content (preferably below 0.002 percent) are observed.

The effect of magnesium is similar to that of aluminum, small amounts (0.004-0.006 percent by weight) having been found to prevent the formation of color.

Table V below lists the results of coating specimen panels according to the process of the invention with zinc containing alloying elements from the group columbium, zirconium, thorium, and mischmetal and the group cadmium, arsenic, copper, lead and chromium. --------------------------------------------------------------------------- TABLE V

Bath Analysis Bath Color Sequence (by weight) Temperature __________________________________________________________________________ Zn-0.1% Cb 500.degree.-650.degree. C. Gold light shades Purple light shades Blue light shades Zn-0.1% Zr 550.degree.-650.degree. C. Gold light shades Purple light shades Blue light shades Zn-2.0% Th 450.degree.-600.degree. C. Yellow light shades Purple light shades Blue light shades Zn-0.5% mischmetal 500.degree.-600.degree. C. Yellow Purple Blue Purple (deep) Zn-5.0-10% Cd 650.degree. C. Yellow light shades Blue light shades Zn-1.5% As 650.degree. C. Yellow Zn-2.7% Cu 650.degree.-700.degree. C. Light Gold Zn-1.0% Pb 700.degree. C. Light Gold Zn-1.0% Cr 625.degree.-700.degree. C. Gold __________________________________________________________________________

Alloy compositions of zinc and titanium, manganese, vanadium, columbium, zirconium, thorium or mischmetal provide colored coatings on steel and pregalvanized materials at temperatures within the range of from about 419.degree. C., i.e., the melting point of the alloy composition, to about 600.degree. C. and above. Alloy composition of zinc and cadmium, arsenic, copper, lead or chromium provide colored coatings on said substrates at temperatures of at least 625.degree. C.

We have also found that the presence of titanium, manganese, or vanadium in amounts of 0.02 percent to about 1 percent by weight in molten tin or in lead-tin alloys containing at least 5 percent tin, permits production of colored coatings by the process of the present invention. With tin, a wide range of attractive colors is produced at temperatures from 280.degree. C. to 520.degree. C., and with lead-tin alloys a suitable temperature range is 320.degree. C. to 500.degree. C. It will be understood that although the description of the process has proceeded with reference to the use of zinc alloys for the provision of colored surfaces, the process of the invention can be used in like manner for the provision of colored surfaces on tin and lead-tin alloys.

The present invention provides a number of advantages. Colors produced by the process and compositions of the invention are reproducible, and can readily be controlled by varying one or more of the following: alloy composition, alloy temperature, temperature of molten alloy surface in a free-oxygen-containing atmosphere, and the time during which the alloy coating remains in its molten and relatively reactive state. Variegated colors, patterns and textures can be produced that provide, in combination, aesthetic effects and corrosion resistant properties. The coatings can be applied to or formed on nonmetallic and metallic substrates, such as ceramics and various metals, particularly steel in the form of sheet, wire and formed articles such as expanded mesh, extruded or cast pipe and structural members. If desired, colored films or foil can be removed from the surface of an alloy bath or the coating can be formed on and removed from a substrate such as graphite to provide thin sheets for decorative uses.

Claims

What we claim as new and desire to protect by Letters Patent of the United States is:

1. A process for the production of a colored surface which comprises melting a metal selected from the group consisting of zinc, tin and lead-tin having an oxygen-avid element effective to produce an oxide film having discernible light interference color effects alloyed therewith to form a molten surface, the alloy so formed having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium, contacting said molten metal surface with a free-oxygen-containing gas for a time sufficient to provide thereon an oxide film and a reflective surface intermediate said oxide film and said alloy having said color effects, and solidifying said molten surface provided with said oxide film and said reflective surface.

2. A process for the production of a colored surface as claimed in claim 1 comprising the steps of applying a metal selected from said group consisting of zinc, tin and lead-tin having a said oxygen-avid element alloyed therewith to an article to form a molten coating thereon, and contacting said molten coating with a free-oxygen-containing gas for a time sufficient to provide an oxide film and a reflective surface intermediate said oxide film and the alloy having said color effects, and solidifying said molten coating provided with said oxide film and said reflective surface.

3. In a process as claimed in claim 2, said oxygen-avid element being selected from the group consisting of titanium, manganese and vanadium.

4. A process for the production of a colored coating on a surface comprising the steps of applying zinc having an oxygen-avid element, selected from the group consisting of titanium, manganese, vanadium, columbium, zirconium, thorium, mischmetal, cadmium, arsenic, copper, lead and chromium and effective to produce an oxide film having discernible light interference color effects, alloyed therewith to said surface to form an adherent molten coating thereon, the alloy so formed having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium, reacting said molten coating with an oxygen-containing atmosphere for a time sufficient to form thereon a film of an oxide of said alloying element and a reflective surface intermediate said oxide film and the alloy having said color effects, and solidifying said molten coating provided with said oxide film and said reflective surface.

5. A process for the production of a colored coating as claimed in claim 4 in which said surface is a metal surface.

6. A process for the production of a colored coating as claimed in claim 4 on a surface comprising the steps of forming a bath of said zinc alloy and applying the zinc alloy to said surface by immersing the surface in said bath to form an adherent molten coating thereon.

7. In a process as claimed in claim 5, said oxygen-avid element being selected from the group consisting of titanium, manganese, vanadium, columbium, zirconium, thorium and mischmetal.

8. In a process as claimed in claim 6, said oxygen-avid element being selected from the group consisting of titanium, manganese, vanadium, columbium, zirconium, thorium and mischmetal.

9. In a process as claimed in claim 7, contacting the molten zinc alloy coating with air for the provision of a film of an oxide of said alloying element.

10. In a process as claimed in claim 8, contacting the molten zinc alloy coating with air for the provision of a film of an oxide of said alloying element.

11. In a process as claimed in claim 7, cooling the molten zinc alloy coating in air for the provision of a film of an oxide of said alloying element.

12. In a process as claimed in claim 8, cooling the molten zinc alloy coating in air for the provision of a film of an oxide of said alloying element.

13. In a process as claimed in claim 5, said oxygen-avid element being selected from the group consisting of cadmium, arsenic, copper, lead and chromium.

14. In a process as claimed in claim 13, contacting the molten zinc alloy coating with air for the provision of a film of an oxide of said alloying element.

15. In a process as claimed in claim 13, cooling the molten zinc alloy coating in air for the provision of a film of an oxide of said alloying element.

16. In a process as claimed in claim 6, said oxygen-avid element being selected from the group consisting of cadmium, arsenic, copper, lead and chromium.

17. In a process as claimed in claim 16, contacting the molten zinc alloy coating with air for the provision of a film of an oxide of said alloying element.

18. In a process as claimed in claim 16, cooling the molten zinc alloy coating in air for the provision of a film of an oxide of said alloying element.

19. In a process for the production of a colored coating on a surface as claimed in claim 4, said zinc alloy consisting essentially of zinc with at least about 0.02 percent by weight manganese, and said molten coating being contacted with a free-oxygen-containing gas for the formation of a manganese oxide film thereon having light-interference color effects.

20. In a process as claimed in claim 19, forming a bath of said zinc alloy and applying the zinc alloy to said surface by dipping said surface in said bath.

21. In a process as claimed in claim 20, said bath having at least about 0.07 percent by weight manganese.

22. In a process for the production of a colored coating on a surface as claimed in claim 4, said zinc alloy consisting essentially of zinc with at least about 0.001 percent by weight titanium, and said molten coating being contacted with a free-oxygen-containing gas for the formation of a titanium oxide film thereon having light-interference color effects.

23. In a process as claimed in claim 22, forming a bath of said zinc alloy and applying said zinc alloy to the surface by dipping said surface therein.

24. In a process as claimed in claim 23, said bath having at least about 0.008 percent by weight titanium.

25. In a process for the production of a colored coating on a surface as claimed in claim 4, said zinc alloy consisting essentially of zinc with at least about 0.001 percent by weight vanadium, and said molten coating being contacted with a free-oxygen-containing gas for the formation of a vanadium oxide film thereon having light-interference color effects.

26. In a process as claimed in claim 25, forming a bath of said zinc alloy and applying the molten zinc alloy to the surface by dipping said surface in said bath.

27. In a process as claimed in claim 26, said bath having at least about 0.075 percent by weight vanadium.

28. In a process as claimed in claim 5, said oxygen-avid element being selected from the group consisting of manganese, titanium and vanadium in amount of from about 0.1 percent by weight to about the respective eutectic composition.

29. In a process as claimed in claim 5, said oxygen-avid element being selected from the group consisting of manganese, titanium and vanadium in amount of from about 0.1 percent by weight to about the solubility limit of the respective element at the bath temperature.

30. In a process as claimed in claim 19, contacting said molten coating with air and concurrently cooling said coating at a controlled rate for obtaining a desired oxide film color.

31. In a process as claimed in claim 22, contacting said molten coating with air and concurrently cooling said coating at a controlled rate for obtaining a desired oxide film color.

32. In a process as claimed in claim 25, contacting said molten coating with air and concurrently cooling said coating at a controlled rate for obtaining a desired oxide film color.

33. In a process as claimed in claim 30, said surface being steel.

34. In a process as claimed in claim 31, said surface being steel.

35. In a process as claimed in claim 32, said surface being steel.

36. A composition of matter in the form of a coating on an article, said coating having a colored surface, said composition consisting essentially of an alloy of zinc and an element selected from the group consisting of titanium, manganese, vanadium, columbium, zirconium, thorium, and mischmetal, a film of an oxide of said alloying element formed on the surface of said alloy and a reflective surface formed on said alloy intermediate said oxide film and said alloy, said alloy having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

37. A composition of matter as claimed in claim 36 having less than 0.0005 percent by weight aluminum.

38. A composition of matter in the form of a coating on an article, said coating having a colored surface, said composition consisting essentially of a zinc base alloy formed from a melt of zinc containing from about 0.0001 percent to about 0.45 percent by weight titanium, a titanium oxide film formed on a surface of the said zinc base alloy, and a reflective surface formed on said alloy intermediate said oxide film and said alloy, said zinc base alloy having less than about 0.002 percent and weight aluminum and less than about 0.006 percent by weight magnesium.

39. In a composition of matter as claimed in claim 38, said zinc base alloy and oxide film together having not less than 0.008 percent by weight titanium and having less than 0.0005 percent by weight aluminum.

40. In a composition of matter as claimed in claim 39, a titanium oxide being essentially in the form of rutile.

41. In a composition of matter as claimed in claim 39, a titanium oxide being essentially in the form of anatase.

42. A composition of matter in the form of a coating on an article, said coating having a colored surface, said composition consisting essentially of a zinc base alloy formed from a melt of zinc containing from about 0.02 percent to about 0.45 percent by weight manganese, a manganese oxide film formed on a surface of the said zinc base alloy, and a reflective surface formed on said alloy intermediate said oxide film and said alloy, said alloy having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

43. In a composition of matter as claimed in claim 42, said zinc base alloy and oxide film together having not less than 0.07 percent by weight manganese and having less than 0.0005 percent by weight aluminum.

44. A composition of matter in the form of a coating on an article, said coating having a colored surface, said composition consisting essentially of a zinc base alloy formed from a melt of zinc containing from about 0.001 percent to about 0.15 percent by weight vanadium, a vanadium oxide film formed on a surface of the said zinc base alloy, and a reflective surface formed on said alloy intermediate said oxide film and said alloy, said alloy having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

45. In a composition of matter as claimed in claim 44, said zinc base alloy and oxide film together having not less than 0.075 percent by weight vanadium and having less than 0.0005 percent by weight aluminum.

46. A composition of matter in the form of a coating on an article, said coating having a colored surface, said composition consisting essentially of a zinc-base alloy formed from a melt of zinc containing not less than 0.1 percent by weight of an element selected from the group consisting of titanium, manganese and vanadium, an oxide film of said element formed on a surface of the said zinc base alloy, and a reflective surface formed on said alloy intermediate said oxide film and said alloy, said alloy having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

47. A composition of matter as claimed in claim 46 having less than 0.005 percent by weight aluminum.

48. In a composition of matter as claimed in claim 46, said oxide film having a substantially uniform thickness within the range of from about 120 A. to about 3,100 A.

49. A composition of matter as claimed in claim 46, said oxide film having a smooth reflecting inner surface formed by the solidification of molten alloy.

50. An article of manufacture having a metallic coating with a colored surface, said coating being integrally bonded to a surface of said article, said coating consisting essentially of a zinc base alloy formed from a melt having not less than 0.1 percent by weight of an element selected from the group consisting of titanium, manganese and vanadium, an oxide film of said element formed on a surface of the said zinc base alloy, and a reflective surface formed on said alloy intermediate said oxide film and said alloy, said alloy having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

51. In an article as claimed in claim 50, said oxide film having a substantially uniform thickness within the range of from about 120 A. to about 3,100 A.

52. An article as claimed in claim 50, said oxide film having a smooth reflecting inner surface formed by the solidification of molten alloy.

53. In an article as claimed in claim 50, said article being formed of a metal.

54. In a metal article according to claim 53, said metal being steel and said coating bonded to said steel by a layer of zinc-iron alloy.

55. An alloy formed as an adherent colored coating on a sheet steel substrate, said alloy consisting essentially of zinc and from about 0.001 percent to about 0.45 percent by weight titanium and having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

56. An alloy formed as an adherent colored coating on a sheet steel substrate, said alloy consisting essentially of zinc and from about 0.02 percent to about 0.45 percent by weight manganese and having less than about 0.002 percent by weight aluminum and less than about 0.004 percent by weight magnesium.

57. An alloy formed as an adherent colored coating on a sheet steel substrate, said alloy consisting essentially of zinc and from about 0.001 percent to about 0.15 percent by weight vanadium and having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

58. A composition of matter in the form of a coating of an article, said coating having a colored surface, said composition consisting essentially of an alloy of tin and an element selected from the group consisting of titanium, manganese and vanadium, a film of an oxide of said alloying element formed on the surface of said alloy, and a reflective surface formed on said alloy intermediate said oxide film and said alloy, said alloy having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

59. A composition of matter in the form of a coating on an article, said coating having a colored surface, said composition consisting essentially of an alloy of lead-tin and an element selected from the group consisting of titanium, manganese and vanadium, a film of an oxide of said alloying element formed on the surface of said alloy, and a reflective surface formed on said alloy intermediate said oxide film and said alloy, said alloy having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

60. An article of manufacture having a metallic coating with a colored surface, said coating being integrally bonded to the surface of said article, said coating consisting essentially of a tin base alloy formed from a melt having not less than 0.02 percent by weight of an element selected from the group consisting of titanium, manganese and vanadium, an oxide film of said element formed on a surface of the said tin base alloy, and a reflective surface formed on said alloy intermediate said oxide film and said alloy, said alloy having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

61. An article of manufacture having a metallic coating with a colored surface, said coating being integrally bonded to a surface of said article, said coating consisting essentially of a lead-tin base alloy formed from a melt having not less than 0.02 percent by weight of an element selected from the group consisting of titanium, manganese and vanadium, an oxide film of said element formed on a surface of the said lead-tin alloy, and a reflective surface formed on said alloy intermediate said oxide film and said alloy, said alloy having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

62. A process for the production of a colored coating on a surface comprising the steps of applying zinc having an oxygen-avid element selected from the group consisting of titanium, manganese, vanadium, columbium, zirconium, thorium, mischmetal, cadmium, arsenic, copper, lead and chromium alloyed therewith to said surface to form a molten adherent coating thereon, said alloy having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium, reacting said molten coating with an oxygen-containing atmosphere for a time sufficient to form on the zinc alloy a film of an oxide of said alloying element having said color effects, and solidifying said molten coating provided with said oxide film to provide a reflective surface on the zinc alloy intermediate said oxide film and said zinc alloy.

63. A process for the production of a colored coating on a surface as claimed in claim 62 comprising the steps of forming a bath of said zinc alloy and applying the zinc alloy to said surface by immersing the surface in said bath to form an adherent molten coating thereon.

64. In a process as claimed in claim 62, said oxygen-avid element being selected from the group consisting of titanium, manganese, aluminum, columbium, zirconium, thorium and mischmetal.

65. In a process as claimed in claim 62, said oxygen-avid element being selected from the group consisting of cadmium, arsenic, copper, lead and chromium.

66. A colored foil comprising a thin sheet of a zinc base alloy formed from melt having not less than 0.1 percent by weight of an element selected from the group consisting of titanium, manganese and vanadium, an oxide film of said element formed on said alloy, and a reflective surface formed on said alloy intermediate said oxide film and said alloy, said alloy having less than about 0.002 percent by weight aluminum and less than about 0.006 percent by weight magnesium.

67. In a process as claimed in claim 6, said bath having a temperature in the range of 420.degree. to 700.degree. C.