I've been adding to my coverage of alchemy bit by bit and came across an alchemy/chemistry project over at The Alchemy Website that you might enjoy trying. It is making purple gold. Colored gold alloys are seen in jewelry and gold is often added to glass to give it color (e.g., ruby glass), but this project is a little different. You'll be performing any of a number of chemical reactions to make a gold chloride solution turn purple.
What You Do
- Mix together a dilute gold chloride solution (0.01%) and a 1% Rochelle salt (potassium sodium tartrate) solution. It's best if you use distilled water to prepare your solutions, as contaminants in tap water may affect your results.
- Another option is to make "Purple of Cassius". This is a purple gold made by introducing tin to a very dilute gold solution. The author of the article posted at The Alchemy Website attempted to produce this color by reacting a dilute solution of gold chloride with stannous chloride. He obtained an amber solution, but not the desired purple coloration.
- Gold may be reduced using formaldehyde. Add some sodium bicarbonate to a gold chloride solution to make the solution alkaline before introducing a drop of formalin.
- Another recipe calls for add a few milliliters of gold chloride to boiling water and then adding some 1% tri-sodium citrate and boiling the solution until the desired color is produced. This colloidal solution is best kept in a shady location, as it is said to be photoreactive.
- In general, gold chloride solution is photoreactive, so you could soak a filter paper with the solution and expose it to sunlight to seek a color change.