I prepared a bottle of Gold Chloride Solution exactly one year ago, well almost, 4/21/11. 1 Gram Chloride in 500 ML Distilled Water. As I only made a half dozen dags over the year, I still have half of the solution left. It has been stored in a full 250ML Amber Bottle in semi darkness(Basement). Does anyone know the shelf life or tried 1 year old solution? I am planning on making some fresh gilding solution from it, but am hesitant to destroy a dag and waste my time. Thank you, Chad
I have used year-old gold chloride stock solution with no noticeable ill effects. But, you should NOT use old sodium thiosulfate solution. If you still have a partial bottle of the sodium thiosulfate stock solution from a year ago (or even a couple months ago), throw it out and mix up a fresh batch, especially if you can detect a rotten egg (sulfur) smell.
Another key to minimizing gilding spots, is to always filter your mixed gilding solution just before use.
Excellent advice Rob, The gold solution keeps for years but thiosulfate is a weak reducing agent and reacts with the oxygen in the air to form sulfate. In time sulfate reducing bacteria can form hydrogen sulfide (rotten egg).
Filtering is a good idea too.
If the gold chloride/thiosulfate solution is too acidic (Ph 2-3), a bit of alkali (Kodak Balanced or dilute NaOH) can be added to raise the Ph to 4-5 for whiter highlights.