Whats with the silver clay bashing... Most of the issues complained about with silver clay are due to under-firing or bad technique, not really the fault of the material... it is certainly possible to produce consistent and good results using silver clay, but like anything you need to go through trial and error to learn what gives a good result. Anyway... agree that the issue here is most likely firing, 15 minutes seems very short, may well be what the pack tells you to do, but experience taught me to ignore the instructions and fire longer for stronger. We use sterling clay and our pieces are fired for about 4 hours. The downside with having one-off silver items cast is the timescales involved with sending to be cast, hallmarked, engraved etc. And castings can also fail, so unless you pay for a mould to be made of each unique piece, which will dent your profits quite some, then you will prob have to re-do the odd wax. In my experience most customers wanting a silver fingerprint charm would not want to wait 6-8 weeks, lots don't like waiting 3-4 weeks