As I understand it, to make gold plate, there needs to be an under layer of nickel. Why does it work to use Aura gold or thin melted gold directly on sterling? Is it because high karat gold doesn’t mingle with the sterling?
I think it is because melted Gold added like this, is significantly thicker than any plating.
you could be referring to gold filled metal. versus gold plated or vermeil. Gold filled is thick gold metal made by bonding gold sheet to an underlying base metal or silver. Gold and silver together if heated will alloy together at the contact as green gold… that won’t be visible on the surface… it you are creating you own sheet out of thick silver and thin gold sheets, fluxing and high heating would be necessary and is very difficult to get it to bond together… I’ve worked in mixed metals with gold wire on silver and vice versa. Using solder is far easier than getting the metals to bond together… even gold filled sheets can be made using a hard silver solder. I don’t advise tiring to bond two sheets together with flux and not using solder. too difficult to get them to stick together without risk of melting…the flux between the sheets also interferes with bonding. Using solder is far easier. Gold also has a higher melting point than silver… sterling melts before high carat gold…even though the gold won’t melt, and the silver is heated below its melting point, there still will be solid state alloy between the two sheets of metal.
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Typically, sheet gold-filled plate (gold outer casing filled by a lesser noble metal) is made in a fine controlled high temperature oven or kiln using a reduction atmosphere to create a ‘fusion weld bond’(1), using only a (carbon-based) gum flux.
In days of old, this was achieved in a blacksmith forge over coal(2), which created the atmosphere by giving off carbon dioxide gas.
(Alternatively, you could use a ‘sweat solder’ with one or both contact surfaces previously coated in solder, held together and reheated.)
If you’re using a gold or silver copper alloy the fusion bonding temperature is lowered proportionately by the copper content percentage.
With pure metals unalloyed with copper, a copper oxide must be applied with the gum.
In answer to your second question, the mixing of metals only occurs if and when both reach their melting temps.
- Untracht, Oppi, ‘Jewellery - Concepts and Technology’ (1982), pp 348/51, 356/7, 367.
- pp 376/7.
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