A client wants me to do a Waterfall Weaving for him, but before he orders he wants a sample of the green copper patina with various light copper browns. He actually sent me a piece of couch fabric to match! Unfortunately, it’s winter in SW Michigan and the shop is on the cool side. Normally I can get a great green on copper patina using Sculpt Nouveau’s Tiffany Green. When it’s 90 degrees, I actually get the beautiful grayish green, the traditional verdigris (‘green of the Greeks’), my favorite. 60-80 degrees and I’m getting fairly neutral greens. Any temperature below 60 and I’m getting bluish greens. This gentleman does not want any bluish-greens. So I’ve been running tests to nail down a reliable (?) patina I can reproduce in the cooler months.
Green on Copper, Browns & Blues – Overview
There are two general ways to achieve patinas – cold (room temperature) technique and hot (200 + degrees) technique. I generally prefer the cold technique because it is more random and varied.
Copper prep: I use a 80 grit sanding pad on the grinder and remove all the copper oxide, stains, etc. from the copper – take it to bright clean metal.
Copper can take on many different colors, depending on the temperature of the patina reaction and which chemicals it has reacted with. Combinations of chemicals often create a variegated patina, which I like best.
Greenish yellow means copper chloride. Note: chloride ion needs to be buffered with something else or it will continue to eat through the copper.
Turquoise blue indicates ammonia has formed a copper-ammonia complex. Very stable. This is the chemical composition or the turquoise gemstones.
Bluish-green: usually ammonia ion plus chloride ion. This is stable – ammonia buffers the chloride ion.
Medium greens: come from many acids, vinegar, sodium chloride (table salt), carbonic acid (from carbon dioxide + water in the air),
Dark green: glacial acetic acid
Golden browns to mid-browns: vinegar, sodium thiosulfate, weak sulfides (liver of sulfur) solution.
Dark brown to black: strong sulfide solutions
Reddish browns – usually acids – nitric acid is a great copper cleaner, but if you leave it on it goes reddish brown (then eventually green)
Green on Copper Chemicals
from the grocery or hardware store
Water – always use distilled, not tap water
Sodium chloride = Table Salt = NaCl
Potassium Chloride = Salt Substitute = KCl
Acetic acid = vinegar (other fruit acids will work, but are generally not so conveniently packaged)
Copper sulfate = CuSO4 = Root Kill (hardware store)
Calcium Chloride = CaCl2 = ice melting crystals
Muriatic Acid = Hydrochloric Acid = HCl (I rarely use this) (paint supplies – used to clean and etch concrete)
from a full-supply Photography shop
Stop Bath = glacial acetic acid (this is very strong & pungent acetic acid)
Hypo = Na2S2O3 = sodium thiosulfate (previously known as sodium hyposulfite)
Tiffany Green patina – I use this a lot. I will try and mix my own and let you know my results in a different post. I believe it includes ammonium chloride, table salt, copper sulfate and possibly zinc chloride.
you can also buy chemicals at a Chemical Supply House – more on that in another post
A Few Copper Green & Brown Formulas and Patinas – Test Results
click on any image to see the full enlarged image
Well, this is confusing. Tiffany Green on raw copper (right side) looks about the same as over the sodium thiosulfate precoated copper (left and middle). Part of the green patina is bluer for the 4 grams of sodium thiosulfate under-patina (left side) and the no undercoat (right side); 8 grams seems to be more neutral. Note the change in appearance when lacquered (right image is lacquered).
left side: Water 2 oz. +
middle: Water 2 oz. +
right side: no precoat
Observation: 4 grams and 8 grams of sodium thiosulfate (in 2 oz. water) give almost identical results, except for slightly more white precipitate (bottom middle) for 8 grams. That could be easily removed with a wet cloth. Note the yellow-green and blue-greens on the left side. This is the Tiffany Green over raw copper, no pre-coat. Note the change in appearance when lacquered (right image is lacquered).
left side: no precoat
middle: Water 2 oz. +
right side: Water 2 oz. +
Vinegar is a great general purpose acid patina, but doesn’t wet the metal well; it tend to bead up. A little nitric acid or table salt can help. Here I used a flat piece of plastic to achieve the same effect. Note how blue the patina became. Browns are lovely though. Note the change in appearance when lacquered (right image is lacquered).
vinegar under mylar – 1 hour
By not drying the vinegar, I am essentially mixing up a patina solution on the surface of the metal. This tends to dilute the Tiffany Green and make it more random. Still quite blue though. More of the transparent greenish-browns because of the dilution effect. Note the change in appearance when lacquered (right image is lacquered).
vinegar under mylar – 1 hour
This one looks like a perfect green on copper for my project – beautiful gray green with lovely golden browns beneath. They don’t want much green, so the transparent brown-greens that appear when lacquer should be perfect. Very dilute liver of sulfur might also work for this effect, in place of the sodium thiosulfate. Note the change in appearance when lacquered (right image is lacquered).
2 oz. water + 2 grams sodium thiosulfate brushed on
This has been a long post, but patinas are complicated, though lots of fun. Hope you have fun with them too! I believe in doing tests and more tests and recording the results.
Further thoughts. Why do I get varying results with the Tiffany Green? Is it the temperature or something else? Generally I don’t shake the 25% concentration Tiffany Green patina before spraying it. Could it be separating slightly in the spray bottle? Specific gravities stratifying in solution? Different chemicals coming out at different times? Maybe that’s my problem. I added ‘Shake!’ labels to the spray bottles. However, separation is very unlikely, as this is a clear solution.
Patina safety – please use gloves! These chemicals can be absorbed through your skin. Fumes usually aren’t a problem though. And don’t breathe any of the chalky patinas – toxic!
Stay tuned for more tests and formulas to achieve the green on copper patina.
Note the change in appearance when lacquered (right image is lacquered). Patinas wetted with water simulate the lacquered look, but not exactly. Thin patinas will look opaque when dry, transparent when lacquered. Lacquers have a big effect on the appearance of patinas.
Why use lacquers? Patinas are often soft and chalky – lacquers make them hard, semi-glossy and non-chalky. Some patinas will wash off when exposed to constant rain or snow – lacquers protect those patinas. Lacquers also help with adhesion of the patinas.
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