|MadSci Network: Chemistry|
Dear Saketh, Blackening feathers or wool (or skin!) with silver nitrate is caused by the formation of silver sulfide Ag2S from the the silver ions and the sulfur in the proteins. Sunlight is not necessary for this, just patience. I never intentionally did such an experiment (but everytime I handled the stuff, I ended up with black fingers). I think the main problem is homogeneous wetting and penetration of the solution into the materials. If you make silver nitrate alkaline with sodium or potassium hydroxide, a precipitate of silver oxide is formed, so this is ruled out. Adding excess AMMONIA (NH3 in H2O) to silver nitrate solution yields a clear alkaline solution, but this can give explosive precipitates with time, and I see no advantage compared with NEUTRAL or very slightly acid silver nitrate. Better wetting may be achieved with an ALCOHOLIC (ethanol) solution of silver nitrate, and blackening is certainly accelerated by heating. Best Regards Werner Sieber
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