Art Metalwork Chapter 6

COLORING AND FINISHING ART METALWORK.

The Coloring and finishing of art metalwork is a very important factor in its success whether viewed from a commercial, artistic, or educational standpoint. It is of importance commercially because articles well colored and finished will sell more readily than those that are not. It is of importance artistically because of the color harmonies and tone values that are involved. It is of importance educationally because of the direct correlation with an important school and industrial subject, namely, chemistry.

Copper has in especially strong affinity for sulphur and oxygen. It combines readily with the moisture and carbon dioxide of the atmosphere to form basic copper carbonate and basic copper chloride. There is no other metal known upon which so many, or so beautiful colors can be produced readily and easily by means of its own compounds. If a piece of copper is cleaned and exposed to the air for a few weeks, it will assume a dark color (frequently called the "Patina") caused by its combination with the oxygen of the air, or with the hydrogen sulphide if soft coal is burned in the neighborhood, or it will turn a green color caused by its combination with the moisture and the carbon dioxide present in the air.
There are three important points to keep in mind when coloring and finishing art metalwork: first, the work must be perfectly clean; second, all of the chemical solutions when not being used must be kept in well corked bottles; third, no matter what color is Obtained the final operation must be to protect and preserve the color by a coat of lacquer or wax.
To color successfully art metalwork, whether copper, brass silver, or gold, one must always keep in mind that the metal must be perfectly clean and free from any trace of oil or grease. Even so slight a thing as the moisture from the hands is a frequent cause of failure along this line. The metal may be cleaned by friction, that is, by rubbing with emery cloth, powdered pumice, or a wire brush, or polishing oil a lathe; or it niay be cleaned by dipping for a few seconds in strong acids.

THE BRIGHT DIPS

When using the "acid dip" method on copper and brass the work must be fastened to a piece of copper or brass wire (do not use iron wire), and hung in the solution for about five to thirty seconds, the length of time depending upon the strength of the solution. The work must then be thoroly washed off in cold running water. Care must be taken to avoid getting any of the solution upon the hands or clothing. A few of the best of these dipping solutions are as follows:
No. 1. Sulphuric acid, one part. Nitric acid, one part.
No. 2. Sulphuric acid, one part. Nitre, one part, Water, one part.
No. 3. Yellow aqua fortis, 1 quart, Sulphuric acid, 1 quart, Muriatic acid, I gill, Water, 1 pint.
No. 4. Sulphuric acid, 1 quart, Nitric acid, 1 pint.
No. 5. Hydrofluoric acid, 4 quarts, Nitric acid, 3 quarts, Common salt, 2 tablespoonfuls.

THE SATIN DIPS

Beside these so called "bright dips" there is another class of dips that are handled in the same way, but give a slightly different result. These are called "satin dips." They are very similar to the bright dips, but in addition they give the work a slightly granulated effect that is known as satin finish. This satin finish may also be obtained by the use of a satin finish wire brush on a lathe revolving at high speed. Some of the acid satin finish dips are are as follows:
No. 1. Hydrofluoric acid, 1 pint, Water, 3 pints.
No. 2. Hydrofluorie acid, 2 pints, Nitric acid, 1 pint, Muriatic acid, one-half pint, Water, 5 pints.
No. 3. Hydrofluoric acid, 1 pint, Nitric acid, one-half pint, Water, 5 pints.
No. 4. Hydrochloric acid, 1 pint, Sulphuric acid, 6 pints, Water, 6 pints.
Immerse the brass in the solution for about r/2 hour.

THE ORMOLU DIP

There is still one other acid dip that is very useful when finishing art metalwork, the "ormolu dip." This dip gives to brass a golden yellow color, and is commonly used on commercial goods
to imitate gold finishes. It is prepared as follows:
No. 1. Nitric acid, 2 pints, Hydrofluoric acid, 2 pints, Zinc scraps, 2 ounces.
No. 2. Sulphurie acid, 2 quarts, Water, one-fourth pint, Nitre, 3 pounds, Add slowly to above solution Muriatic acid, 1 quart.
As hydrofluoric acid will dissolve glass or crockery, any solution, that has hydrofluoric acid in it should be kept in a jar that has been painted thoroly on the inside with Sapolin or asphaltum varnish.
After any one of the preceding bright satin or ormolu dips has been used on art metalwork, the work should be immediately dried and lacquered by dipping in banana oil, or it should be warmed and coated with a thin coating of Johnson's black furniture wax, and then lightly polished with a soft cloth when it is cold.

COLORING SOLUTIONS

There are many recipes for obtaining various color effects upon copper, some of which are expensive and difficult to handle, and others require considerable skill in their application. Some of the standard and easily applied (simple immersion) coloring solutions for use on copper are as follows:
No. 1. Antique or Oxidized Copper. Dissolve about one cubic inch of potassium sulphide in one pint of water, add six drops of ammonia, and apply to the copper; if the color is too dark add more water. When it is dry, polish with emery cloth in one direction only to relieve the color and bring out the design; then lacquer or wax.
No. 2. Another antique finish on copper that gives a more varigated color effect is as follows: In one pint of water dissolve one fourth of a teaspoonful of barium sulphide. Clean the article thoroly and wash in cold water; while it is still wet apply the barium sulphide solution. Various results can be obtained by making the solution weaker or stronger. When it is dry, finish by lacquering or waxing.
No. 3. Brown color on copper, shading to black according strength of solution: in one pint of water dissolve five drachms of nitrate of iron.
No. 4. Potassium sulphide three ounces; ammonia, ounce; water, one gallon. Immerse the articles.
No. 5. Dark brown on copper: one pint of water, five drachms of nitrate of iron, and two drachms of potassium sulphocyanide.
No. 6. Brown on copper dissolve one ounce of sal alnuloniac and one-third of an ounce of oxalate of potash in one-half pint Vinegar. Immerse and apply with a cloth.
NO. 7. Dark brown : in one pint of water dissolve one ounce of sulphate of copper, one ounce of hyposulphate of soda, two drachms of hydrochloric acid.
No. 8. Red shading to brown, according to strength of solution : in one pint of water dissolve one drachm of pearl ash, and one drachm of sulphur.
No. 9. Red: one pint of water, two drachms of sulphide of arsenic, one ounce of pearl ash.
No. 10. Steel gray: in one pint of water dissolve one drachm of chloride of arsenic. Bring the solution nearly to the boiling point and immerse the articles in it.
No. 11. Various colors may be obtained by means of the fol lowing solution : dissolve in one quart of water three hundred grains of acetate of lead, and six hundred grains of hyposulphite of soda. After the solution is dissolved, heat to the boiling point and immerse the articles. The first color produced is gray, continued baths will produce violet, maroon, red, and finally steel blue.
No . 12. There is also the very interesting method of coloring copper by heat. In this method no chemicals of any kind are used; all that is necessary is that the metal shall be perfectly clean and that it be slowely passed to and fro thru a blue gas flame, such as is obtained from a Bunsen burner or any ordinary gas stove. It is also possible to get results from other heating methods such as a clear hard coal fire, but the trouble with such methods is that the article is very liable to get smoked. The colors obtained by the heat method come in this order if it is done slowly : First, orange
red; Second, bluish purple; Third, brassy color; Fortth, dark red;
Fifth, deep purple; Sixth, iridescent; Seventh, chestnut color.
The first two colors partially come off when the lacquer or wax is
applied. All the others are permanent if they are lacquered or waxed.
The lacquer is applied as soon as the article is cold, the wax while it is still warm. Care must be taken when obtaining the chestnut color not to pass it into the flame any more when the chestrlut color begins to come, because if the chestnut color is carried too far the color will flake off and the entire process of cleaning and coloring will have to be repeated.
No. 13. For a dead black finish on copper immerse in this solution : water, 5 quarts; one fourth pound sulphate of potasium; two ounces of concentrated
spirits of sal ammoniac.
No 14. A steel-Grey dipping solution for copper is as follows: dissolve four ounces of muriate or arsenic in two quarts water.
Use hot.