how to determine exposure time?

Roli · Post by **Roli** » Sat May 01, 2004 8:10 am

Hi everybody,

last nightsession was a success!
Yesterday I´ve got new material from Slavich (PFG-01 - film-roll) and it worked perfectly.

It seems that 4 years for PFG-01 plates are to much - I think I´ve stored it wrong - maybe the plates got some white light.
Thank you all for the infos!!!!

Cheers
Roli from Salzburg

Michael Harrison · Post by **Michael Harrison** » Sat May 01, 2004 8:17 am

The age of your material is as important as any other element. How were you storing it?

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If someone says it can't be done but they haven't tried it, don't believe them.
http://www.dragonseye.com/Holography

Bob · Post by **Bob** » Sat May 01, 2004 11:47 am

Ya learn somethin' new every day! 8^) Please excuse my Amerocentric perspective.

JohnFP · Post by **JohnFP** » Sat May 01, 2004 1:48 pm

Glad to hear it. Welcome to the worderful world of holography!!!

Jeff · Post by **Jeff** » Sat May 01, 2004 3:15 pm

".. How about adding 1g/L of EDTA to a reversal bleach, would that "solve" the problem? "
It would'nt be satisfactory because if you had a satisfactory silver halide solvent added to a solvent bleach it would start at once to dissolve up your virginal fine grain silver halide that you need to see your hologram. EDTA is excellent for complexing to almost any metal ions but silver ions are ones it does least well with. But then you cannot add a bit of good silver halide solvent such as hypo to very acid dichromate bleach or it will instantly oxidize.
Actually Colin there is something to be said for your idea in the form of a treatment post dichromate bath. If you have a slight scatter caused by just silver chloride from tap water chloride then a very mild silver halide solvemt such as sodium sulfite solution or possibly EDTA could after a brief rinse remove silver chloride but leave the much less soluble silver bromide in your fringes pretty much untouched. It can be worth trying this on milkiness problem holograms. You need to do some trial and error tests on the concentration of sulfite and the immersion time Im afraid.

I have found that you can clean up a hologram with this problem if it is only a mild case of it by just running it under a hot tap (~70C) for a minute or 2. Yes it does remove a bit of wanted AgHal but the final colour shift to a shorter wavelength can be a compensation to the eye.
Jeff

Tom B. · Post by **Tom B.** » Sat May 01, 2004 11:09 pm

Thanks! I had not really thought about how bleach in the emulsion might interact with tapwater contaminants AFTER bleaching. Sometimes I might have noticed a slight reduction in the brightness of the transmission holo seen in swollen reflection holos after tapwater rinse - maybe that would explain it. I will definitely try adding a post-bleach presoak in distilled water before tapwater rinse to my development ritual.

Martin · Post by **Martin** » Sun May 02, 2004 3:40 am

No problem.

Martin · Post by **Martin** » Sun May 02, 2004 3:41 am

Thanks for explaining the subtleties of dichromate reversal bleaching.
Regarding the problem you mentioned ("... prevent dissolved up silver from redepositing ..."), tricks taken from the laundry chemistry wouldn't work neither? I am thinking of Calgon (sodium hexametaphosphate) or zeolites? Or adding a small amount of a colloid (maybe PVA) to the bleach?