U of S | Mailing List Archive | alt-photo-process-l | Re: white precipitate in VDB

Re: white precipitate in VDB

On Sun, 2 Mar 2008, Christina Z. Anderson wrote:

Anyway, this is it--"the sensitizing solution must be made with distilled water, because the silver nitrate will react with chlorine and hard water ions such as carbonates, etc., that exist in many water supplies. The result is a cloudy white precipitate of silver chloride, silver carbonate, etc...."

Now, the last two times I mixed up VDB solution I definitely used distilled water from the grocery store, not "spring" water or some other option, so perhaps this is why I don't experience the problem, not because I heat my water up. The fact, as Judy says, that some "distilled" waters are not, in fact, distilled really kinda creeps me out. I mean, one can imagine that happens in 3rd world countries but on our own grocery shelves?
One other relevant afterthought... recalling Joachim's supposition that to cause precipitate upon mixing or similar failure, the water would have to be so awful you could smell it down the block, it occurred to me that the trouble given for tapwater is not stinky (decomposition of organic matter I presume) but *metallic* -- that is, things like mercury or lead, which can leach into the water from the pipes themselves or the soldering/joints, or groundwater from local contamination, etc., and are not detected by taste or odor.

However, those are among the ingredients wells are tested for ... We don't get scare headlines that water from the soandso well stank -- everyone would know that and it would be corrected pronto. They'd fish the dead cat out ! (Tho that's facetious -- I wouldn't hazard a guess about what it would take to make well water stink.)

The bad news usually comes as a surprise, that such and such % of mercury, lead, or whatever was found by testing. (I recall that mercury in water sources was one of the scandals early in George W. Bush's first term, when his appointee running the EPA raised the allowable amount.)

And I seem to recall that it's contact with other metal (as metal caps on containers we're always warned against, or metal pots or instruments) that causes failure in the mix. Hence the failures with unfiltered tap water.

I do not know or pretend to know or hope to ever know the mechanism, I simply pull from memory of discourse and memory of experience (as memory fails daily but is not yet obliterated) a series of factoids which seem to me to offer an explanation:

Tap water could have those contaminants which we do not taste; distilled water wouldn't.