Gold paint is most probably composed of tiny flakes of gold leaf-flat, very thin plates that remain 'float' in suspension but are large enough to reflect true gold color. A gold precipitate, depending on the size of the gold particles, can, and usually does not appear golden. Just like when polishing, say sterling silver, with a cloth, the cloth turns black. This is because of the visible light reflecting from the very fine particles is trapped within the slurry; and essentially no light IS reflected-the visible wavelengths are 'caught' by the mixture of very small silver particles, silver tarnish, and granules of the polishing compound. (Polishing perfectly clean silver results in black as well, as does polishing brass, steel, etc.)
So, to make gold paint powder the gold needs to be precipitated-or joined into larger masses-perhaps not easily possible-or formed somehow into larger (still micro-scale) masses, and then flattened for best effectand gold reflection, perhaps by flattening between two highly polished very hard substances; two diamond surfaces come to mind, or a hard ceramic--or, maybe even Corelle Ware if its surfaces are flat enough. Again, the extremely small precipitant particles will reflect light among themselves trapping most or all of the visible light and therefore not appear gold, but any color (brown in your case) to the no color, black.
[An easier method for making small gold flakes just occurred to me which is much easier than 'squashing' gold:
Paint the pure fine mixture of gold precipitate on a high gloss, or gold-rejecting very heat resistant substance, say a ceramic tile, then heat the tile with Mapp gas or oxyacetylene, electric, whatever, above the melting point. A solution-actually just a suspended mixture of washed gold precipitate-in an acceptable layer thickness when dried will agglutinate, the micro particles will unite and form flakes. However, with many ceramics the gold will stick-fuse to the surface and one will end up with a beautifully gold-flaked tile. But, some substances do not 'like' gold, and the gold can be brushed or scraped off. Finding these refractory materials should not be hard; I would start with the high temperature silicones (not silicon or silicate). At the worst you can have a 24 carat tile, which you may want to dissolve the gold from and began again. Please wear face protection and, Good luck!]
Paint the pure fine mixture of gold precipitate on a high gloss, or gold-rejecting very heat resistant substance, say a ceramic tile, then heat the tile with Mapp gas or oxyacetylene, electric, whatever, above the melting point. A solution-actually just a suspended mixture of washed gold precipitate-in an acceptable layer thickness when dried will agglutinate, the micro particles will unite and form flakes. However, with many ceramics the gold will stick-fuse to the surface and one will end up with a beautifully gold-flaked tile. But, some substances do not 'like' gold, and the gold can be brushed or scraped off. Finding these refractory materials should not be hard; I would start with the high temperature silicones (not silicon or silicate). At the worst you can have a 24 carat tile, which you may want to dissolve the gold from and began again. Please wear face protection and, Good luck!]
