I have been making salt prints for some time now and use hypo for fixing. Using Wynn White's method I use a 10% solution. Occassionally, very occassionally, I get very small blotches in the highlights after some 6 - 12 months. I have just realised that the hypo I buy is anhydrous - I am wondering whether I am using anhydrous in a crystalline recipe and therefore over-fixing(which I understand can be detrimental, although I'm not sure in what way). So the question is; if I read a recipe which contains sod. thio. which do you think the recipe would mean -- anhydrous or crystalline? Also if the crystals clump in the container does that suggest it is then unusable?