BRONZE CASTING PROCESS: POST 9
PATINA
I hope you all have stayed well, and that you keep finding things to do that you love doing. In times like these, which are of a kind none of us have been through before, I guess we just keep as busy as possible eating Cheetos and sharing drinks on Zoom! And we keep looking forward to the day we don’t hear the word “coronavirus”, because it isn’t around anymore. But these can be motivating times too; times to contemplate running at large like a pack of wet dogs, the minute we are free to run again, slobbering and drooling and blubbering to our heart's content, licking surfaces and jumping into peoples' laps!
Now, on to the fascinating world of patina.
When I have a sculpture sanded and ready for the patina it has a dull brassy look. The textures are muted or obscured by the monotony of color and lack of highlights that would appear if one were to polish the bronze to a high luster. When polished, bronze has a very beautiful color and feel, not unlike gold, but it is not very good at retaining its luster. Over a fairly short period of time the shiny surface will dull, and darken with a natural, but boring patina. But since I can, I want my pieces to look ancient, as though they have been salvaged from the depths of the Aegean Sea, lost in time, yet with the natural colors of oxidized copper that occur only under certain conditions.
Over many years I have developed a process of chemical patination that I worried I would never master. And I was right to worry! It is imprecise, and it can get away from me, but I more or less get what I want these days. I use a few chemicals that are common in the business, and if it isn't blue, green, black, or brown, or more likely, all of the above, I probably didn't make it. To paint a bronze object pink or red or any number of colors brings to me the question, “Why was the object made of bronze?” Why not plastic or even iron or pot metal? If the bronze composition of the object is of importance to the value, it should be evident. Otherwise, to me it's like making an extraordinary automobile out of gold, because that is what is most valuable, but then painting it with a vinyl paint in such a fashion that it is indistinguishable from a fiberglass or sheet steel car. A spiffy paint job does not lend value when applied over a superior surface, which bronze is, in my thinking.
The colorations that are achieved by chemical patinas are generally protected by wax or lacquer. I prefer wax, but it isn't very good for outdoors. Indoors, kept from the sun's rays, a chemically patinated bronze will keep its colors for a good long time. Eventually, due to one circumstance or another, most bronze objects will darken to a brown or black, or maybe a fairly brilliant green, with the right environment. Often they develop a combination of the three colors, with the brown being places where there is some contact with people, such as cleaning of the surface, or people rubbing against it, the greens occurring from acids like those found in air pollution and animal droppings, often concentrating in deep textures, and in streaks where the most run-off occurs in a rain. The black areas will be those less trafficked by handling, and yet not areas that rain funnels toward. Fortunately most people like the way bronze ages, so the aging isn't very often something we wish had not happened. Rarely is an old bronze improved by any kind of cleaning, and is probably best off just being dusted and rubbed with a soft cloth now and then. If it gets especially filthy, it is a job for someone who knows what they are doing to clean it up, and even then it is likely that the person doing the cleaning still will wish they were dead before they succeed at making it look as good as it did when they started.
I use four chemicals for patina; Ferric nitrate, cupric nitrate, sulfurated potash and ammonia. Ferric makes reds and browns, cupric, greens and blues, sulfur, black and gray, and ammonia washes cupric into the deeper textures. My patinas take hours, playing a torch flame across the piece to get the right temperatures for the chemicals to color the surfaces. Each chemical is mixed in a solution with water,
and applied by brush or spray bottle. Cupric will not do much if the metal it lands on isn’t hot. Too hot, and it burns to black. Too cold and it looks like copper foil, and is unstable. Just right, it turns the metal blue.
Ferric over cupric makes yellows to browns, and cupric over ferric makes greens and eventually blues if laid on thick enough. Sulfur turns all of the chemicals black, as well as turning bare metal black. It is a tarnish, and as such is useful primarily in darkening the pale color of bronze from yellowish to black. Other chemicals are usually applied over the top of sulfur-treated metal.
I usually spray my pieces with a light fog of ammonia to settle the cupric into the deep textures, as I like the enhanced depth it creates on the surface. When the piece is cold, and dry, I wax it with Johnson’s Paste Wax and buff it after the wax dries.
So, this is a good time for anyone following along here to go to the bathroom, or get another gin and tonic. I am about to dive deep into the weeds of the more esoteric elements of bronze sculpting. Just kidding. It is time to reward yourself for the patience you have demonstrated to slog through my series of posts on process, or maybe to shoot me an email about how much of your perfectly good time I’ve wasted. Either way, enough is enough, and I thank you for your patience. I hope this has been informative and only slightly exhausting. I know I'm exhausted, and I haven't even read it!
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