Need Help with Printwasher Design

[Robert McClure]

I'd just like to get some basic ideas for building a simple printwasher. I am relatively handy and understand the basic requirements. In my case I will be washing both 8x20 and 8x10 prints. I have been simply tray-washing so far.

The general idea as I understand it is plexiglass sheets to form the appropriate "slots."
Granted, the plexiglass sheets need to be affixed in some fashion, say, to the inside of the larger container.

I saw one washer which was both the tank portion, plus a (submersible) rack for the prints. Water in-flow at the top of the tank, water exit at the bottom.

On one site I saw where someone had affixed plexiglass dividers to the inside of a small glass fish aquarium tank. Seemed pretty crude but apparently worked.

I understand that the virtue of a "washer," (the supply water coming in from the top with an equal volume of water constantly leaving the washer from a tube at the bottom) is:

1. that water usage is reduced greatly because
2. the washing function is more efficient, i.e., water is more completely utilized to more completely remove unwanted chemical residues.

I would ask, what am I missing here? It seems pretty simple, at least concept-wise. Or am I embarking on something too difficult/tricky to mess with, myself?

You help greatly appreciated.

Robert

[paulr]

Washers can be pretty simple. The most important thing is that you have a reasonably even flow over the whole surface of all the prints. You don't want stagnant water to accumulate on any one edge or corner. You could probably check this with food coloring, but I don't know what design principles you'd use to encourage even flow.

The flow rate can be very, very slow. You're not really washing the prints, you're soaking them, allowing thiosulfate ions to diffuse out of the paper and into the water. The only purpose of the flow is to make sure there's always water present at the prints surface that has a lower ion concentration than the paper itself. That's really all there is to it.

There are no advantages to designs where water enters the top and leaves the bottom. That was thought up by someone with a genius for marketing, but a few gaps in their understanding of basic chemistry. There are also no advantages to designs that fill the water with air bubbles. Except that they're more fun to watch.

[Colin Graham]

Also keep in mind that plexiglass is very expensive right now. I just made a washer but only because I got a bunch of 1/4" plexi for free. Only a little more expensive to buy a used one on ebay.

[John Kasaian]

I'm not sure what the prices are up to these days, but Versalabs were very reasonable back when I bought mine and a built of amazingly tough plastics.

[Robert McClure]

Many thanks Paul, Colin, and John. This helps. And yes, I will be keeping a lookout for used.

Regards

[Greg Lockrey]

I made one out of stainless and have a stainless tubing at the bottom with holes every half inch pointed toward the bottom at about 30 degrees both sides to throw agitation down which will eventullay rise to the top. At the top I have spill holes. The sheets of film hang in their respective holders. Because of the direction of flow, the film is steady and gets more than enough random agitation. The hard part was getting the tubing into a Y shape and getting a good leakproof weld to the outside where I hook up a garden type hose to a faucet.

[Neal Wydra]

Dear Robert,

Consider using opaque PVC sheets from www.mcmaster.com. Much cheaper than plexiglass and bonds easily.

[Michael Daily]

What would one use to bond PVC sheet to acrylic (plexiglass)? I plan to do the same thing.
Michael

[Jfnphotography]

I'm working on a print washer, I used a 40mm or 80mm ammo can (big enough for 11 x 14 prints ) from a army surplus store as my container, the ammo cans are, skinny and tall so they don't take up a lot of space. I have room for about 6 prints. I used 1/4" plexi for my divides. Took directions from Darkroomsource but did some modifications. I didn't want to drill into the ammo can so I ran a 1/2 tube to the bottom of the can, and use gravity to pull the water out and into the sink. I also took plexi and made holder for my divides. so I didn't have to glue the dividers in, I tried it out this weekend and it worked great.
Jacob