I've read all the threads and precautions on making silver nitrate but the cost here in Israel is just too high to buy it (300$ for 100g or 200$ for 50g of silver nitrate for pure 99+% grade). There is nitric acid in our studio (for etching) and 925 silver (sterling?) can be easily obtained. A few questions before I begin:

1. Can the nitric acid be warmed with bain-marie to haste the process instead of using a hot plate? This will be performed outside so having electricity can be a problem.

2. Is 92.5% of silver nitrate enough for various alternative processes (collodion/salt paper/...) or should it be refined? I'm not planing on manufacturing Kodak grade products, just experimenting with old photographic processes.

3. If it does need to be refined, what is the best/easiest way? Copper wire?

4. On perfect conditions, one should use 75g of silver per 100ml of nitric acid to convert all the acid to H2O and NO (which converts to NO2 with air?). This should yield about 1.57g of silver nitrate per 1g of silver. Does refining silver yields a much lower values or roughly the same as pure silver in the solution?