If you are going to or have started making dry tin types there is a better developer additive I have found. It is Ammonium thyocyanate, but this one is different for some reason. It gives clearer shadow areas and does not give off a strong ammonia smell like the other kind I was using. I have abandoned the potassium thyocyanate. The image tone will be more tan than grey and the exposure about double,at least that has been my experience. Develop 90 sec.- 2 min. Experiment! It can be purchased from Elemental Scientific (elementalscientific.net) and is not expensive. They also have a really good selection of inexpencive glass wear. Request a catalog with your order, it might take a while for the order to get to you but be patient, it took almost a month for mine but I used a check.