If I am understanding your question correctly, you melt down old candles to make yours? If that's the case, there is no way to know that all the candles are the same. Yes, you may be using the same molds, but the actual wax that you are using (the remelted wax) may all be of different age/quality. The only thing I would use old candles like that for is for testing molds, layering, so on, and MAYBE, to use chips to tint my candles. Aside from that, pick yourself up a tester kit from any other the online retailers or your local craft store. They range in price, but you can typically get your feet wet and your head on straight for a reasonable amount out of pocket. HTH Tristan