MadSci Network: Chemistry

Re: dyeing ( black) with silver nitrate

Date: Mon Jun 26 10:41:48 2000
Posted By: Werner Sieber, Research Scientist, Pigment Division, Ciba Specialty Chemicals Corp.
Area of science: Chemistry
ID: 961772521.Ch

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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