US1951304A - Method of coloring copper and copper alloys - Google Patents

Description

Patented Mar. 13, 1934 UNITED STATES METHOD OF COLORING COPPER AND COPPER ALLOYS John It. Freeman, in, Cheshire, Kirby, West Cheshire, Conn.,

and Philip H. assignors, by

mesne assignments, to Copper and Brass Research Association, New York, N. Y., a voluntary association of New York No Drawing. Application J anuary.-20, 1932, Serial No. 587,754

9 Claims.

This invention relates to the coloring of copper and copper alloys, and has for its object the production on copper and alloys. of copper of .a

pleasing color or patina, in particular, a green coloration.

Copper and copper alloys, such as copper roofs and ornamental bronzes are widely used. It is known that copper and its alloys when exposed to the atmosphere will in time due to natural weathering take on a pleasing green coloration- The rate at which copper and copper alloys 25 take on or acquire a natural green coloration or patina varies greatly according to atmospheric conditions and requires in any case a period of years to develop.

Numerous previous attempts have been made 36) to rapidly develop the patina or green color by treatment with various chemicals and mixtures of chemicals. Green coloration may be ,developed quite readily by such treatment but we have found that coloring so produced by any 33 method known to us is not permanent, the coloring washing off gradually in rain storms giving the surfaces that have been treated a streaked and unsightly appearance.

We have found by chemical analysis of .sam-,

ples of patina scraped from samples of old copper roofs taken from the railway station at Providence, R. I., and from the Yale University Library at New Haven, Conn., and other samples that the patina or green coloration that develops on copper and copper alloys, such for example as alloys of copper and zinc, by natural weathering is principally the chemical, basic sulfate of copper. This compound when formed by natural weathering on the surface of copper or copper 59 alloys is adherent and is insoluble in water and so is permanent. The reason previous methods of producing patina on copper have failed is that the chemical formula and solutions were not of such nature as to cause to be formed on the copper the basic sulfate such as is formed by natural weathering, it-having always been believed by previous workers that the patina was a basic car bonate of copper which they therefore attempted to reproduce.

What we have discovered therefore and wish to secure by Letters Patent is the production by suitable treatment on the surface of copper of an adherent and permanent patina, or more particularly an adherent and permanent green coloration which is of similar chemical composition to the basic sulfate of copper that develops by natural weathering after exposure to the atmosphere for a period of years. The chemical compound known as basic sulfate of copper that is formed by natural weathering on copper or copw per alloy surfaces is of a complex nature and may exist in different forms, but corresponds in general in chemical constitution to the formula CuSO4.3Cu(OH2). Similarly the patina that we produce by accelerated means may exist in different forms but is essentially of the same constitution as the patina that forms by natural weather- We have found that to obtain the most satisfactory patina or green coloration on copper and its alloys, such for example as the brasses and bronzes, although we are not limited to these alloys, having suitable adherence and uniformity, that it is best produced by alternate immersion of the article of copper or copper'alloy to be colored in a solution of ammonium sulfate. Sim-= ilar coloring may be obtained by other means such as repeated or continuous spraying or swabbing with a solution of ammonium sulfate or any means by which the copper or copper alloy surface is made to come in contact with a solution of ammonium sulfate and oxygen either as such or as it exists in the atmosphere.

In our preferred method the article or articles to be colored are dipped in a solution of ammonium sulfate for sufiicient time to permit the solution to moisten thoroughly all parts of the surface to be colored and then are withdrawn from the solution and permitted to remain in contact with theair to permit oxidation attack by the oxygen of the air. I

This cycle of alternate dipping into the solution and oxidation by the atmosphere is repeated until the desired coloring or patina is obtained.

The solution 1 is prepared by dissolving ammonium sulfate in water. A pure grade of ammonium sulfate may be desirable for some purposes but for reasons of economy less pure grades such as used for fertilizer may be used and satisfactory results obtained. We prefer to use a inc concentration of about 5 to 10% ammonium sulfate in water but diluted or highly concentrated solutions or that is solutions of any concentration may be used. We find it of advantage to heat the solution to from about 50 C.- C. In order to hasten the process but it maybe done with the solution cold. The process may be hastened by maintaining the atmosphere to which the articles are subjected during the oxidation phase of. the process in a highly humid condition but this is not necessary to obtaingood results. An atmosphere of pure oxygen instead of the normal atmosphere containing only about 20% oxygen may be used.

The length of time that the article is in the solution and in the air will depend upon comvplexity of design and size of the part to be colored and other factors such as temperature, concentration of solution and humidity of the oxidizing atmosphere.

We have found a period of about 4 seconds in a 10% solution of ammonium sulfate at 50 C. and 2 minutes in the air to give satisfactory results.

Under some conditions of treatment it is found that the color obtained is a darker green than that which develops by natural weathering. This darker shade is due probably to the retention in the patina formed of certain copper-ammonium compounds. These salts or impurities may be removed and the more normal shade of green obtained by subjecting the article to a hot humid atmosphere for such length of time as is found necessary to obtain the desired shade, such for example as'an atmosphere of a temperature above 30 C. and more or less saturated with moisture. I Having thus set forth the nature of our invention, what we claim is:

1. The method of producing on the surface of copper and copper alloys an adherent green coloration of patina similar in character to that which forms due to natural weathering after a period of I time which comprises treating the copper or copper alloy surfaces with a solution of ammonium sulfate and thereafter exposing to oxygen.

2. The method of producing'on the surface of copper and copper alloys of an adherent green coloration or patina similar in character with that which forms due to natural weathering after a period of time which comprises alternately immersing the copper or copper alloy surfaces in a solution of ammonium sulfate and exposing them to an oxidizing atmosphere.

3. A method of producing on the surface of copper or copper alloys 9. green coloration or patina which comprises alternately moistening the s' faces of the copper or copper alloy article to be colored by an ammonium sulfate solution and subjecting it to the action of oxygen.

4'. A method of producing on the surface of copper'and copper alloys an adherent green coloration or patina which comprises alternately dipping the surfaces to be colored in a 2 to 15% water solution of ammonium sulfate and then subjecting to oxidizingaction of the atmosphere.

5. A method of producing on the surface of copper or copper alloys a green coloration or patina which comprises alternately immersing the surfaces to be colored in a solution, maintained at an elevated temperature, containing about 10% ammonium sulfate for such period of time as to permit the surfaces to be wet by the solution and then withdrawing the surfaces from the solution and letting them be exposed to a humid atmosphere for sufiicient length of time to permit oxidizing action to occur, the cycle of alternate wetting by the solution andoxidation by the atmosphere being repeated a suflicient number of times to produce the depth of coloring desired.

6. The method of producing on the surface of copper and copper alloys of an adherent green coloration or patina similar in character with that which forms due to natural weathering after a period of time which comprises wetting the copper or copper-alloy surfaces with a solution of ammonium sulfate while exposed to an oxidizing atmosphere.

7. The method of producing by accelerated means on the surface of copper and copper alloys of an adherent green coloration or patina similar in character with that which forms due to natural weathering after a period of time Which comprises alternately wetting the copper or copper alloy surface with a water solution of ammonium sulfate and letting it remain in contact with the air to permit oxidizing action to occur.

8. A method of producing on the surface of copper or copper alloys an adherent green coloration or patina which comprises alternately moistening the surface to be colored with a 2 to 15% water solution of ammonium sulfate and subjecting to the oxidizing action of the atmosphere.

9. A method of producing on the surface of copper and copper alloys an adherent green coloration or patina which comprises alternately dipping the surfaces to be colored in a 2 to 15% water solution of ammonium sulfate and then subjecting to the action of oxygen.

JOHN R. FREEMAN, JR. PHILIP H. KIRBY.