Home made print washergreenspun.com : LUSENET : Large format photography : One Thread
In a moment of enthusiasm I built one of David Vestal's "el-cheapo" print washers, somewhat modified to be exact. Problem: Air bubbles form on the print. I assume that is not good. How do the 'real' washers avoid that? I have never seen one in operation. Do they use some scheme to make turbulence that prevents it?
-- Richard C. Trochlil (email@example.com), March 23, 2002
With my Versalab I take the rack and tap it against the bottom several times to dislodge bubbles that form when the tank is filling. After the tank is filled, I dont get any more bubbles. If you are, your problem might not be in the washer but further up the line
And no, that is not good because the bubble spots wont get washed.
-- Wayne (firstname.lastname@example.org), March 23, 2002.
Air bubbles on prints are caused by disolved oxygen in the water; especially in cold winter water (cold water can disolve more oxygen than warm water); and water with Hardness levels of about 100 parts per million (ppm) or more. I draw my water from Lake Michigan and ,in the winter, have the same problem in my store bought washer. What I do is, from time to time, through the wash cycle, tap, shake and wiggle the washer as the bubbles form. Then wait for summer when there is some other problem to deal with.
-- Howard Anderson (email@example.com), March 24, 2002.
Actually the oxigen answer is incorrect. Let me clarify this, in Summner water degasses more oxigen and in winter the water keeps the oxigen in solution because of the lower temperature, this ranges from 6 ppm in summner to 10 ppm in winter, not enough to cause air bubbles, where Howard was partially correct was thinking of water hardness. The bubbles are formed by Carbon Dioxide which is generated when water with some hardness comes in contact with an acidic medium to generate carbonic acid which decomposes into carbon dioxide when the ph is raised, and you get to see the little bubbles....Think, high ph (developer) low ph (stop bath) low ph (fixer) then high ph (wash water) thus you can see why you are generating the bubbles. I do this for a living purifing water for nuclear plants etc, and it is part of my job to remove Oxigen and CO2. In any case, if you wish to remove the bubbles you would have to lower the ph to below 4 to keep the carbonate in acid form, not something you really want to do. So to answer your question yes the idea is to generate sufficient turbulence to prevent the bubble from forming on the print, if they form on the sides of the glass who cares?
-- Jorge Gasteazoro (firstname.lastname@example.org), March 24, 2002.