Chemical coloring of metals
[3] Another example of early chemical coloring of metals is the Nebra sky disk, which has a green patina and gold inlays.
An early example of black colored iron is the famous Celtic spearhead found in the River Thames and dated between 200 and 50 BC.
[4][5] Pliny the Elder mentioned the distinction between naturally occurring and artificial patina in the first century CE.
[6] Another ancient document about the chemical coloring of metals is the Leyden papyrus X (3rd century CE).
Zosimos of Panopolis, a Greek-Egyptian alchemist who lived in the late 3rd and early 4th centuries,is also extremely important, since to him attributed texts are considered to be the oldest written recipes for chemical coloring of metals.
[8] Patination is also briefly mentioned by Italian painter and writer Giorgio Vasari and by Pomponius Gauricus in his work De Sculptura 1504.
André Felibien also briefly mentions some techniques for patination of bronze sculptures in his work Principes in 1699.
[10] Leonhard Elsner, Alexander Watt, Antoine César Becquerel (1788–1878) and Rudolf Christian Böttger (1806–1881) are also important people in the early history of electrochemical coloring of metals.
Great progress was made in the industrial application of chemical coloring of metals in the early 20th century.
After the Second World War, there was a growing interest in green patinated copper sheets, which were intended primarily for architectural use.
[24][25] Chemical coloring of metals is primarily used in the manufacture of sculptures, jewelry, badges, medals,clocks, watches and decorations.
Black for silver Items are immersed in a 2.5% solution of potassium or sodium sulfide, after the appearance of the color wash objects well and wax or varnish it.
[26] Green for copper and its alloys Paint or spray objects with a solution of 250 grams of ammonium carbonate / 250 grams of ammonium chloride / 1 litre of water, each layer is dried for 24 hours, after reaching the desired shade wax or lacquer it.
The object is coated with a solution, after 24 hours it is rubbed with coarse cloth or finest steel wool, the process is repeated at least three times, finally, the material should be wiped with a greasy rag.
[30] Black for aluminum Boil a solution of 20 g ammonium molybdate and 5 g of sodium thiosulfate in a liter of water, immerse the objects, rinse, dry, wax or lacquer after the development of color.
[31] Lustre colours Use a solution of 280 g of sodium thiosulphate, 25 g of cupric acetate and 30 g of citric acid.
[32] Variant for tin and pewter: 250 g sodium thiosulphate, 60 g copper acetate, 25 mL acetone, 1 L water, 45-85 °C, 1–20 minutes, gold -pink -blue - green.
[33] Variant for stainless steel: 100 g sodium thiosulphate, 10 g lead acetate, 12 g potassium sodium tartrate, 12 g copper sulfate, 1 lit water, 18-22 °C temperature of solution, 5–50 minutes, yellow, brown, red, green, blue, violet, object must be in contact with piece of copper 300 times smaller surface than surface of treated object.
[34] Different colors on titanium As a simple electrolyte, it is possible to use a 3% solution of trisodium phosphate, a cathode of stainless steel, object as anode.
[36] According to one Chinese patent, treated objects can be then immersed in a hot diluted sodium silicate solution (1-5%,95-100 C,3-10 min.).
[37] Hexavalent chromates are carcinogenic and toxic, molybdate-based solutions are now being proposed as a substitute (for example molybdate 30-100g/boric acid 10-18 g/manganese sulfate 0.5-5 g /1 litre water.
