Quote Originally Posted by pstake View Post
This is a very attractive quality! Until Gerald posted that you could use bicarbonate instead of sodium hydroxide, I had never heard of this recipe. Maybe I should order Thiocarbamide after all...
Note that Gerald posted a Carbonate based mixture, not a Bicarbonate based one. If you add Bicarbonate to Carbonate, you form a Carbonate/Bicarbonate buffer which lets you reliably achieve buffered pH values between about 9 and 11. This is about the range where Thiourea based sulfur toner goes from dark brown (pH 11+) to very light yellow (~pH 9).

Quote Originally Posted by pstake View Post
It does raise the question for me, though, as to why you can't adjust the pH of the sulfur solution using bicarbonate, and control the tone?
I have no idea how Sulfide based toner would respond to pH changes, but would strongly advise you against experiments. H2S, which will be released in quantity if you are not sufficienty alkaline, is about as toxic as HCN, and your nose will not smell it if concentration of H2S in the air is above a certain level! If you insist on using Sulfide based toner, please follow well reviewed recipes to the letter unless you have a fully equipped chem lab at your disposal.