Heat coloring of metals is a relatively simple process that, in principle, produces interference colors on the surface of the metal. The colors depend on the temperature to which the metal is heated. The most obvious example is thermally produced colors on steel, of which blue coloring is most commonly used. In addition to steel, colors can be produced by heat on copper and its alloys, nickel, chromium, niobium, titanium, and tantalum.
Heat coloring of metals can also include procedures for obtaining brown or black color by gradually heating objects made of gilt copper (also known as vernis brun) or steel coated with linseed oil to 300–400 °C.Jochem Wolters: Techniken und historische Merkmale des Braunfirnisses – eine Richtigstellung. In: Jahrbuch des Römisch-Germanischen Zentralmuseums Mainz / Römisch-Germanisches Zentralmuseum. Bd. 57(2010), 1, Verlag des Römisch-Germanischen Zentralmuseums, Mainz 2010.Theophili que et Rugerus presbyteri et monachi libri III. De Diversis Artibus: seu Diversarum artium schedula. (translation R. Hendrie), London 1847, p. 319.
This process also includes the Bower–Barff process and related processes, in which the steel is heated to 800 °C and exposed to highly heated steam.Silman, H. Chemical and electroplated finishes, London 1948, p. 160.The Bower–Barff Rustless Iron Process, New York 1883.
History Heat coloring of metals is probably the oldest method of coloring metal objects.Fishlock, D. Metal Colouring, Teddington 1962., p. 64
Examples
Heat coloring of iron and steel
straw yellow: 232 °C brown: 265 °C purple red: 277 °C light blue: 288 °C dark blue: 293 °CKraemer, O.P. Rezepte fuer die Metallfaerbung und Metalleuberzuege ohne Stromquelle, Saulgau 1983, p. 82.
Heat coloring of stainless steel
light yellow: 290 °C brown: 390 °C magenta: 450 °C blue: 540 °C dark blue: 600 °C
Heat coloring of titanium
pale gold straw: 385 °C purple:412 °C deep blue: 440 °C red purple: 565 °C light green: 510 °C brown gray: 648 °C green blue: 925 °CUntracht, O. Jewelry Concepts and Technology, New York 1982.
Heat coloring of copper and its alloys
Heating to a temperature of 161–341 °C produces various interference colors, ranging from pale yellow, red, violet, and finally black. Unlike steel, this patina is non-permanent and more tedious.Untracht, O. Metal techniques for craftsmen, New York 1968, p. 419.
Literature
See also Chemical coloring of metals Electrochemical coloring of metals Black oxide Bluing (steel) Anodizing
References
External links Lewton Brain, C.: Patinas for small studios (pdf-file), 1985 Budija, G.: Collection of formulas for the chemical, electrochemical and heat colouring of metals, the cyanide free immersion plating and electroplating (), Zagreb 2026 Heat tinting stainless steel