View Full Version : Archival Washer Design

Matthew Hoag
17-Jan-2002, 19:00
I am building a vertical print washer from scratch and wanted to know if the wat er intake should be on the bottom or top and the outflow be on the bottom or top . I heard that fixer is heavier than water so the outflow shoudl be on the bott om???? Any truth to this? Thanks all.

N Dhananjay
17-Jan-2002, 19:43
I remember Richard Henry (Controls in B&W Photography) pretty much scoffing at this notion. I tend to agree with him. These are not two immiscible liquids. Its one solution of fix dissolved in water. So what matters is having a lower concentration of fix in the water sorrounding the print than the concentration of fix in the emulsion of the print (i.e., a gradient in the concentration). This enables fix to diffuse out of the emulsion. So, you need to remove some water to keep the concentration in the water sorrounding the print lower. Caveat: this is my surmise based upon what I know at this point - don't claim to have done any testing or anything of the kind. If I'm off base on this, I'm sure others will chime in. Cheers, DJ.

Pete Caluori
17-Jan-2002, 19:43

The density of fixer is greater than water, but in the quantities present in an archival washer insignificant. Water intake can be from the top, or side, but it really doesn't matter as long as there is sufficient movement in the washer, i.e. no dead spots where water doesn't circulate. The circulation of water doesn't have to be great, it just needs to occur. Outflow is best siphoned from the bottom. By siphoning, the washer will remain full should you loose your supply.

Regards, Pete

N Dhananjay
17-Jan-2002, 20:20
Don't mean to butt in again, but if this is true, the most logical design for a washer would be to hold the print flat just below the surface of the water - fix would diffuse out and sink to the bottom (since its density is heavier than water and the fix and water are supposedly immiscible). So there would be clean water sorrounding the print again (since the print is not near the bottom but being held near the top, just under the surface of the water). So, more fix would diffuse out and sink to the bottom again. No change of water required and no circulation of water required. Over a period of time, all the fix would diffuse out and sink to the bottom. Like I say, the idea of fix being heavier etc is, in my opinion, a bit of lore (Henry seems to suggest that this was some clever marketing hyperbole by Picker, who knows?).

Fixer is nothing but chemicals dissolved in water. As such, its distribution would tend to be uniform throughout the solution of water. What is more important therefore is establishing a gradient of concentration to enable continuous diffusion out of the print and into the water. To do this, all that needs to be done is to remove some of the water at a uniform rate. This also explains why you do not want dead spots (since that would reduce the diffusion out of the emulsion locally). But once the fix diffuses out of the emulsion, it will pretty much evenly be distributed throughout the solution.

Cheers, DJ

Ellis Vener
17-Jan-2002, 21:45
take a look at the very ingenious Gravity Works film washer design. basically what happens is that when the tank fills up to a cetain extent any extra water beyond that starts a very rapid syphon action that empties the entire tank. If you have ever had to syphon gas you'll understand the principle.

Conrad Hoffman
18-Jan-2002, 01:29
PT did an article on this some time back and I remember the conclusion was that the "fixer is heavier" argument doesn't hold water. I have an older stainless vertical print washer where they drilled a small hole near the bottom to insure that the heavier fixer was flushed out. Oh well. You don't want any stagnant areas, but that same argument applies- it's almost impossible for an area to avoid water exchange if there's any reasonable flow. Add a bit of dye to the water (no prints!) to prove it to yourself.

Scott Walton
18-Jan-2002, 11:41
Go to:http://www.cyberbeach.net/~dbardell/darkroom.html and scroll down to the print washers. I would imagine if you emailed him he would discuss how he made them out of aquariums.