This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
A perfect substitute for dead gilding cannot be obtained by bronzing, because of the radically different reflection of the light, for the matt gilding presents to the light a perfectly smooth surface, while in bronzing every little scale of bronze reflects the light in a different direction. In consequenceyof this diffusion of light, all bronzing, even the best executed, is somewhat darker and dimmer than leaf gilding. This dimness, it is true, extends over the whole surface, and therefore is not perceptible to the layman, and cannot be called an evil, as the genuine leaf gold is so spotted that a bronzed surface is cleaner than a gilt one. The following process is the best known at present: Choose only the best bronze, which is first prepared thick with pure spirit. Next add a quantity of water and stir again. After the precipitation, which occurs promptly, the water is poured off and renewed repeatedly by fresh water. When the spirit has been washed out again in this manner, the remaining deposit, i. e., the bronze, is thinned with clean, good gold size. The bronze must be thin enough just to cover. The moldings are coated twice, the second time commencing at the opposite end. Under no circumstances should the dry, dead gilding give off color when grasping it firmly. If it does that, either the size is inferior or the solution too weak or the mixture too thick.
Five parts of prime dammar rosin and 1.5 parts of ammonia soda, very finely pulverized. Heat gently, with frequent stirring, until the evolution of carbonic acid ceases. Then take from the fire, and when cool pulverize again. Put the powder into a glass carboy, and pour over it 50 parts of carbon tetrachloride; let this stand for 2 days, stirring frequently, then filter. Ten parts of the fluid are to be mixed with each 5 parts of metallic bronze of any desired shade, and put into bottles. Shake the tincture well before using.
Take bronze and stir with it pale copal varnish diluted one-half with turpentine. With this paint the ornaments neatly. In 0.5 hour the bronze will have dried. The places from which the bronze is to be removed, i. e., where the bronze has overrun the polished surface, are dabbed with a small rag soaked with kerosene, taking care that it is not too wet, so as to prevent the kerosene from running into the ornament. After a short while the bronze will have dissolved and can be wiped off with a soft rag. If this does not remove it entirely, dab and wipe again. Finally finish wiping with an especially soft, clean rag. Kerosene does not attack polish on wood. The bronze must become dull and yet adhere firmly, under which condition it has a hardened color. If it does not become dull the varnish is too strong and should be diluted with turpentine.
To render bronzes durable on banners, etc., the ground must be primed with gum arable and a little glycerine. Then apply the bronze solution, prepared with dammar and one-tenth varnish. Instead of gum arabic with glycerine, gelatine glue may also be employed as an underlay. .