Lustful brew
A luster brew (from Italian lustro for gloss and brew hot solution) is a solution for coloring metal surfaces .
Luster brew always contains one or more heavy metals that form stable colored sulfides . Most often a lead (II) compound or a copper salt ( sulfate , acetate or tartrate ) is used. Thiosulfate is very often used, which allows the sulfide to be separated out relatively slowly. A classic lead-based recipe is:
- 120 g / l sodium thiosulphate
- 40 g / l lead (II) acetate
In contrast to patination solutions for copper and bronze e.g. B. sulphide-based, which react directly with the copper of the base material to form colored sulphides, a metal is added to the luster brew, which is deposited on the surface and allows metal surfaces such as brass to be colored, on which the direct coloring fails.
The working temperature is usually 60–70 ° C, the exposure time ranges from seconds to minutes. There are also luster brew compositions that act cold (with process times of hours).
Luscious brews deposit thin sulfide or oxide layers on the surface, the thickness of which increases with the exposure time. The colors are created by the interference of light waves and successively go through different tones from golden yellow to red, red-violet, steel blue, light blue to light gray. The metal surface must be thoroughly cleaned and degreased before coloring (for example with Viennese lime ). Only then can the objects be brought into the dye bath. All metals are suitable for coloring ( aluminum only to a limited extent), but above all copper and brass . The golden yellow coloring of brass is also known as false or French gilding.
Individual evidence
- ↑ H. Krause: metal coloring . 3. Edition. C. Hanser, Munich 1951.
- ^ Anne Moncrieff, Richard Hughes, Michael Rowe: The Coloring, Bronzing and Patination of Metals . In: Studies in Conservation . tape 30 , no. 4 , November 1985, pp. 193 , doi : 10.2307 / 1506046 .