Hello
@pentaxuser, price of Kala Namak does vary with brand and so does the Sulfide content. However, I don't think there is any correlation between price and Sulfide content. No need to go for higher priced brands thinking that they will have higher Sulfide content. I suggest you first try a reasonably priced brand like the one Niranjan suggested. Regarding Sulfide content, the scientific study I shared in OP shows that all the salts they analyzed had good amount of Sulfide though the exact amount varied from brand to brand. In your specific case, if you go with the brand Niranjan suggested, you should be fine as he has tested it.
Kala Namak is safe for humans and can be stored and mixed in the kitchen. In contrast Thiourea is not safe for humans and should be kept away from the reach of children. As far as fogging paper and film is concerned, Thiourea dust can do just that and hence mixing needs to be done in a well ventilated area away from the place where film and paper are stored. And that place is certainly not the kitchen. Whether Kala Namak will fog film and paper stored in safe box or black bag when in solution is something I don't know. Quite unlikely that the toner solution will fog when stored in stoppered bottle. Not so sure when it is in open tray. If you or someone is interested in finding out, they can do some controlled tests and share the findings with the rest of us. That way you can extend the knowledge about Kala Namak toner.
