Im thinking of building a slot processor for 20 x 24 prints- kind of a rolling floor model.. I have a good handle on the design and fabrication but I'm in doubt about one thing- is there a corrosive factor between B&W chemistry and ordinary hardware store type plexiglass? Is there some reason we don't see plexi used for this more often?

Chris

-- Chris (cyeager@ix.netcom.com), April 29, 2002

Answers

Chris:

Acrylic plastics (Plexiglass, Acrylite, etc) are totally inactive to working strength black & white chemistry. I have been making my own tanks, trays, and washers out of the stuff for well over 20 years. My 220 roll film tanks have probably processed over 1000 rolls by now, never once have I had a problem with either the film or the tanks.

One caution: full strength acetic acid will react with acrylics, so make sure you mix your stop bath in a separate container. Also; don't leave water in them for looooong periods of time (several weeks), as the joints may degrade a bit.

Acrylics are good plastics for this sort of thing, but don't underestimate the weight of the liquids in a 20x24 unit.... the sides may be prone to bulge out. I suspect that 1/2 inch thick sides will bulge unless reinforced with extra bracing. I made a 12-slot 16x20 washer that holds about 20 gallons (167 lbs, plus the washer itself), and I had to reinforce the 1/2" sides. 1/4" dividers will probaly survive bulging.... if you fill them simultaneously. Have fun.

-- Reinhold Schable (rschable@quik.com), April 29, 2002.

Thanks for the answer- Im going to try to limit the capacity by making the slots V-shaped, tapering at the bottom... this will look less like a print washer and more like my Nova trimate- with its separate compartments- |V-V-V| So I'm hoping this way to minimize stress on the sides- they'll be butressed though..

chris

-- Chris (cyeager@ix.netcom.com), April 29, 2002.

One should not use the slot processor as a place to mix chemical... Even if it is not acetic acid. I did it without knowing, trying to dilute developer concentrate in the slot. I found it VERY difficult to agitate to make uniform working solution, and it took a while of detective work. I threw away a tankful of chemical to mix a fresh one out of raw chemicals just to realize the chemicals dumped to the sink was perfectly fine though it was not working at all in the slot when tested with small test strip.) By the way, it is best to chose formulae that have large processing capacity for use in slot processors because changing solution is cumbersome. I use BUFFERED stop bath because unbuffered acetic acid stop bath is way too acidic at the beginning yet its capacity isn't as large as mildly buffered version.

-- Ryuji Suzuki (rsuzuki@rs.cncdsl.com), May 02, 2002.