[kailee33]

Hi all, sorry, not a chemist here but hoping for some input on a project I have. I work with pottery and im currently attempting to create my own gold lustre glaze, just looking for a little help on the chemical processes involved. Research via pottery papers and books can only take me so far. The process is as follows.

A salt of gold, likely AuCl4 is dissolved in a resin, typically pine resin and a carrier oil like eucalyptus. This oil gives a medium in which can be painted directly to pottery, but also helps in a localised reduction on the piece. This localised reduction can produce some very desirable effects when using certain base metals like tin, copper, bismuth etc but I dont really see the need on a gold glaze, therefore Im sure its sole purpose is just as a carrier.

Now I have a few questions?

Ive been told in modern lustre glazes they use a different salt of gold, is there any other gold salt which is highly soluble which could be used in place of AuCl4? Ive saw a modern recipe which is a vivid red colour when applying.

Most recipes ive found for the reduction of metals salts follow the same format as described above, but the only references ive found to making a gold lustre describes using "Balm of Sulphur" which is a mix of linseed oil & elemental sulphur. I understand that sulphur dioxide can reduce gold salts but I'm a bit at a loss in why it would be employed in this situation.

The general temperature these things reach in the kiln is around 750C, so would the gold chloride not reduce by itself with heat alone?

One safety sheet I have found refers to gold pinanyl mercaptide as a main constituent, but I'm assuming this is just way of describing gold chloride in resin?

Sorry for the basic questions, I have ran some tests but obviously would like a deeper understanding of what's going on before I pour £££'s into experimenting more.

[Hunter2]

There not many gold salts available. HAuCl4 or AuCl3 are the Standards. Others are like KAu(CN)2 are poisson.
The reduction can be done with other metals and organic materials like ascorbic acid.

[Corribus]

Citrate is probably the most used reductant of gold salts.

[Hunter2]

Yes especially to produce gold nano particles.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987575/

[kailee33]

There not many gold salts available. HAuCl4 or AuCl3 are the Standards. Others are like KAu(CN)2 are poisson.
The reduction can be done with other metals and organic materials like ascorbic acid.

Thanks Hunter, yeah, i did stumble across the poisonous salts, I doubt these would be used in a pottery environment

Well, I can see the various methods of reducing gold salts with SMB and various other chemicals, but it would appear the first choice back in the late 19th century was by adding sulphur to the resin, when heated the sulphur would convert to dioxide, and reduce the salt. But I'm a little confused, surely gold chloride will reduce without any additions when heated to 750C?

[Borek]

Thanks Hunter, yeah, i did stumble across the poisonous salts, I doubt these would be used in a pottery environment

Actually I wouldn't be surprised at all.

Some substances used in chemistry/industry/craft are toxic, but they are often reasonably safe when used with some standard precautions, and - what is the most important part - the final product is perfectly safe. If there is also no toxic waste accompanying the process there is no reason to avoid these substances.