Hi, You can use any brand of Bleach (I think you have to mix with a little water and leave for about 10mins or so) it doesn't go quite as black as the professional liquids, but it works.
I have to say I agree with this method. I wear a large turquoise
ring that was myfirst attempt at setting a stone and making a ring.
I’ve worn it for two years daily and it developed a nice blacking
patina while I wasdisinfecting cages at the wildlife center. This
ring goes thru alot on my hand and the black has stayed in the
crevices. The high points became shining with continued wear and it
looks perfect.