Replies

1. 
   saschafer | May 07, 2009 03:15am | #1

   At room temperature and normal atmospheric pressure, ammonia is a gas. The bottled ammonia that you buy is actually ammonia dissolved in water. As long as the solution is kept inside a closed container, the gas goes back into solution as fast as it comes out, and so the amount of ammonia stays the same. As soon as you expose the solution to the ambient, the ammonia starts coming out of solution. That's what you smell, and that's why fuming works.

   So yes, the ammonia solution becomes weaker with use, as the ammonia escapes. Eventually, it will become so weak that it can't emit enough ammonia to do a decent job of fuming. If you fume your piece for a short time, say, an hour or two, then the strength of the remaining solution will not have been depleted very much, and it will work fine the next time. But if you fume your piece for a long time, a day or more, then you're getting into the territory where there's a significant decrease in the amount of ammonia. You can keep reusing it, but you'll reach a point when it's not doing the job, and then you'll have to replace it. Fortunately, you can just fume the piece some more with fresh ammonia.

   Rather than put the used ammonia back in the bottle with the fresh ammonia, you're better off using two bottles, one for the fresh ammonia and one for the partially spent but still usable stuff. That way, you'll know that you always have some "good" ammonia, in case the used stuff is too far gone.

   -Steve

1. 
   tjwheeler | May 07, 2009 03:28am | #2

   Thanks, Steve.  Makes sense - practical.     Tom