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Hey Guys,

When I prepair glass sometimes I get a beautiful sheathing action as I pull the glass out of the last DI bath. The water on the plate just evenlt cascades off. An there are some days I don't. These times the water pulls together and bunches up. I normally will have to go back and windex the plates before using.

What are some of the factors that control this?

I first wash the glass with warm water and dishwashing soap then rinse, then soak the glass in Muratic Acid 3%, then wash it with soap and water and again, then into a DI tank until I am ready to use it.

If a glass plate soaks for a week can it get so saturated with water that it effects the surface tension? Dumb question but the only factor I can think of.

Thanks all

Pure clean glass should reject water. That is, I think that when the water beads-up, rather than sheeting, that an indication that the glass is clean. If DI water sheets off of the glass either the glass has some surface contaminant that attracts the water, or else the water itself has some wetting agent (perhaps some residual soap). I have never done DCG so the next question may be stupid, but why do you wash the glass with soap then treat with muriatic acid, then wash with soap a second time? In my opinion you might be better off washing with soap, then treating with acid, then rinsing well with DI water skipping the second soap wash (or maybe rinsing well with tap water to dilute the acid and THEN giving a final rinse in DI water to conserve the DI). Worth a try?

The surface of glass strongly attracts water. Glass in ordinary environments already has a layer of water adsorbed to its surface. There's a German paper on glass (highly relevant to the DCG holographer) called "The Glass Surface and Ways of Its Modification." I couldn't provide a direct link to this .pdf paper, but just Google the title, and it will appear.

Thanks DJ

rzeheb wrote:I have never done DCG so the next question may be stupid, but why do you wash the glass with soap then treat with muriatic acid, then wash with soap a second time? In my opinion you might be better off washing with soap, then treating with acid, then rinsing well with DI water skipping the second soap wash (or maybe rinsing well with tap water to dilute the acid and THEN giving a final rinse in DI water to conserve the DI). Worth a try?

Good question, after I pulled the glass out of the MA bath I saw it was not sheating well so I give another wash.

I read the link but not sure what I should get out of it?

Thanks all!

Have you tried to correlate the pH?

The final thing I do when I clean glass is dry them with a 1/4 paper towl, the ones that separate in 1/4's. I do this because having cleaned glass windows I notice that no matter how clean you think they are, a nice rub with a slightly damp paper towel makes them cleaner. The slight damp is the water drops left on the plate. So now, back to my point. I notice when I rub the glass with the towel there is a noticable difference between both sides. One is very smooth and one rough, probably from the glass being float glass. So if you turn your glass over does the other side act differently?

If you think glass is clean, dip it into a bucket of water. Then shake salt over the glass. If the salt is not even you were not clean. If salt won't stick there the water has gone because the glass was not clean.

I always use glass from photoframes. Last time I bought 40 plates from 2 different brands, 20 of each. Of the one brand, all plates cleaned well, nice hydrophylic surface, no beading at all. Of the other brand, about half the plates were not clean even after soaking overnight in pure bleach + double soap wash. My guess is that some batches of glass have impurities that make the surface hydrophobic, just like when treated with rainex. Plates I treated with rainex remain totally hydrophobic even with pure bleach treatment. The hydrophobic groups are chemically bonded to the surface and apparently very inert.