[napoleon]

i have recently ordered some ferric nitrate crystals to be used for etching sterling silver. I am a little concerned however with some of the info i have come across about the explosive nature of ferric nitrate when in contact with oxidising materials (and apparantly some metals). I am an artist, not a chemist and would appreciate an informative but simplified explanation of the risks that may be involved in using the stuff. I understand the corrosive nature of the product but its really just the self combusting issues that concerns me. My options are few for etching sterling silver and i have used nitric acid in the past but really sont want to touch the stuff anymore. Ferric Nitrate seems to be the next best thing. Can someone please help.. Many thanks

[woelen]

Don't worry too much about the explosive nature of ferric nitrate. it indeed can form mixtures, which can ignite and are self-sustaining once ignited, but this only can occur, when it is mixed with reducing agents (e.g. sulphur, carbon powder, aluminium powder) and when it is used in the solid state.

I assume that you use an aqueous solution of this compound. In that case there is not much risk at all. In fact, ferric salts are used for etching purposes quite a lot (I use ferric chloride for copper etching). The reason that you need ferric nitrate is that you are using it for silver etching. Silver would give an impermeable layer of silver chloride with ferric chloride. Silver nitrate is soluble in water, so that works quite well.

The only real risk is with spent solutions. Solutions of ferric nitrate only are slightly toxic, but the spent solution is much more toxic, due to dissolved silver. The waste definitely must be brought to a proper waste processing facility.