This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
For all patinas, whether the ordinary brown of commerce, the green of the Barye bronzes, or the dark-orange tint of the Florentine bronzes, a brush is used with pigments varying according to the shade desired and applied to the metal after it is warmed. Recipes are to be met with on every hand that have not been patented. But the details of the operation are the important thing, and often the effect is produced by a handicraft which it is difficult to penetrate.
A dark tint may be obtained by cleaning the object and applying a coat of hydrosulphate of ammonia; then, after drying it, by rubbing with a brush smeared with red chalk and plumbago. The copper may also be moistened with a dilute solution of chloride of platina and warmed slightly, or still by plunging it in a warm solution of the hydroehlorate of antimony. For the verde antique a solution is recommended composed of 200 grams of acetic acid of 8° strength, the same quantity of common vinegar, 30 parts, by weight, of carbonate of ammonia; 10 parts, by weight, of sea salt; with the same quantities of cream of tartar and acetate of copper and a little water. To obtain the bronze of medals several processes afford a selection: For example, the piece may be dipped in a bath consisting of equal parts of the perchloride and the sesquiazotate of iron, warming to the evaporation of the liquid, and rubbing with a waxed brush.
Dissolve copper nitrate, 10 parts, by weight, and kitchen salt, 2 parts, in 500 parts of water and add a solution of ammonium acetate obtained by neutralization of 10 parts of officinal spirit of sal ammoniac with acetic acid to a faintly acid reaction, and filling up with water to 500 parts. Immerse the bronze, allow to dry, brush off superficially and repeat this until the desired shade of color has been obtained.
Sodium chloride. 37 parts
Ammonia water. . 75 parts
Ammonium chloride .......... 37 parts
Strong wine vinegar..........5,000 parts
Mix and dissolve. Apply to object to be treated, with a camel's-hair pencil. Repeat the operation until the desired shade of green is reached.
Oxalic acid....... 5 parts
Ammonium chloride ........... 10 parts
Acetic acid, 30 per cent dilution. . .. 500 parts
Mix and dissolve. Use as above indicated. The following will produce the same result:
acid.......... 4 parts
Ammonium chloride ..........16 - 17 parts
Vinegar containing 6 per cent of acetic acid.....1,000 parts
Bluish Green.—After using the first formula (for green) pencil over with the following solution:
Ammonium chloride .......... 40 parts
Ammonium carbonate........ 120 parts
Mix and dissolve.
V.—Potassium sulphure........ 5 parts
Mix and dissolve. With this, pencil over object to be treated, let dry, then pencil over with 10 parts a mixture of a saturated solution of ammonia water and acetic acid and 5 parts of ammonium chloride thinned with 1,000 parts of water. Let dry again, then brush off well. Repeat, if necessary, until the desired hue is attained.
VI.—Corrosive sublimate. 25 parts
Potassium nitrate.. 86 parts
Borax............ 56 parts
Zinc oxide........ 113 parts
Copper acetate . . .220-225 parts
Mix and heat together on the surface of the object under treatment.
Brown.—The following is a Parisian method of producing a beautiful deep brown:
Potassium oxalate, acid ........... 3 parts
Ammonium chloride ........... 15 parts
Water, distilled..... 280 parts
Mix and dissolve. The object is penciled over with this several times, each time allowing the solution to dry before putting on any more. The process is slow, but makes an elegant finish.