distilled vs. reverse osmosis

[robert_4927]

Thanks, I'm sure that is the case Jorge. The meter although brand new is a hand held Milwaukee. It has an accuracy of +or- 2% f.s. ( whatever f.s. is?) The first thing we did was calibrate in the solution provided with the meter. The reading from the RO system is 0 but as you said the meter must not be sensitive enough .It claims to read from 0 - 1990. I left the probe in long enough to reach the same temp as the water even tried moving it around in different areas of the container trying to get a reading of more than 0 and still can not get it to read any higher. I don't know if I'd attempt to reduce platinum or mix ferric oxalate with RO water but I think it will work well enough for mixing developers, toners, and clearing baths.

[Sal Santamaura]

"(whatever f.s. is?)"

Full scale. In this case, +/- 2% of 1990, or +/-39.8

[Arne Croell]

Dan, both ion exchange and RO remove ions, although through different processes, and not all ions (a standard ion exchanger, like that in certain dishwashers, replaces some ions (Fe, Mg, Ca etc.) with sodium ions) . The TDS measurement actually relies on the charge of ions in the water. The lab setup I was referring to actually uses first an ion exchanger and then a multiple stage RO unit to arrive at the ultrapure 18MegOhm water.

[brook]

The RO water I had the trouble with was purchased from a grocrey store with the RO unit on site. If memory can be trusted it was called double reverse osmosis.
That said, I regularly make up other film developers with plain old tap water, and fresh D-23 has proven to be near fool proof ( and I, if anyone, can give fool proof a run for the money). Pyrogallol based developers seem to be espically finicky, ABC being the most prone to problems in my experience. I have made Pyrocat HD stock solutions from tap water with perfectly good results. On a practical level, unless you really have a thing for 1890's pyro formulas, I bet your results will be fine.
Brook

[robert_4927]

I just used the RO water to reduce sodium chloroplatinate (NA2) from 20% solution to a 5%solution. Now this may be so minute that I can't tell but there is no difference in the way the solution reacts to the print in comparison to the solution made with the distilled water. But I agree, we're talking drops here so why chance it...use the distilled. One other note....I was at the grocery store and went to grab a bottle of distilled. And lo and behold you have to watch the distilled water. Some jugs if you read the fine print are steam distilled and others are reverse osmosis distilled. And here I thought distilled meant steam....In large print the one reads....Giant Eagle Distilled Water....the fine print reads....bottled at the source: Alpine natural springs process by filtration, reverse osmosis.

[robert_4927]

brook, all i use is pyro developers, wd2d+ and pyrocatHD.....You mean there are other types of developers? (lol)

[Calamity Jane]

But . . . but . . . but . . .

. . . if you don't use distilled water, how do you explain to the revenuers why there's a still bubbling away in your basement : - 0

[Steve Bell]

Dan, you mentioned "I haven't heard of anyone using Deionized water for photographic chemical processing." I've checked all around here, no one sells distilled water anymore. All I can get is deionised water intended for topping up batteries, electric irons etc. As this used to be distilled in the past, I thought it was the same. As we have very hard chalky water here I intended to use it along with a wetting agent for the final wash of 4x5 FP4+. Will this be a worthwhile improvement over tap water?

[Dan Dozer]

Arne - I'm curious what part of the country you are in. I work as a specialty design consultant on high technology laboratory facilities. However, I'm not an expert on the plumbing system designs - I'm only an architect. I'm only asking because the typical system setup on my projects has standard filter cartridges first, then through the RO system to a storage tank, then to the Deionization system and circulated through the building. 18 MegOhms is standard as it leaves the DI unit. Your experience is that the DI and RO units are reversed. I wonder what the pros and cons are for each approach?

Steve - back to the photography stuff. I can still get distilled water around here, but the supply seems to be shrinking. I wasn't aware of the differences that Robert indicates whether it is steam distilled or RO distilled, but I'm now going to pay more attention. I just checked a jug I bought last week and it says steam distilled. I would also think that just about any type of purfied water for film washing purposes would be better than normal tap water. Laboratory users use deionized water when rinsing their glass ware to reduce the possiblity of water spots on the glass when it dries. The same should hold true for film and you might find out that you don't even need the wetting agent at all.

[Charlie Skelton]

As an aside, I remember a joke in New Scientist where someone in conversation dropped in " Everything I know about semi-permeable membranes, I picked up by a form of osmosis".

Cheers

Charlie.