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RobertJSherman
27-Jan-2019, 09:48
I've been looking for an answer to this one for a while - when preparing glass plates and applying a gelatin sizing it is said to use chromealum - the challenge is the ratio is almost never mentioned. My copy of the Alterntive Process text doesn't seem to specify the dilution - should it be a 10% or 20% solution? Maybe it doesn't matter . . .

If you know what resource is available that identifies the best practice for this chemical, I'd love to get my hands on it -

thanks.

Pere Casals
27-Jan-2019, 10:42
Robert, IMHO, I think it doesn't matter much. The important thing is having the glass perfectly clean, with absolutely no grease, so don't touch surface anymore after cleaning.

Wash very well with dishwashing soap, rinse very well with tap water and make a final bath in distilled water (mixed with everclear until 50% if you want faster drying).

In theory a chrome allum bath may leave some little residue on the plate that would harden (if pH was also the rigth one) the gelatin layer in contact with glass, but I found that irrelevant as I add chrome allum in the emulsion finals. The most important is that the plate is completely clean, this is nothing on glass but air, because of that final bath in distilled water is good.

My experience is that I get the same with a chrome allum treatment than with a perfectly clean plate, other's may see a benefit from the C-A... of course. Just try it, see what happens with 10%, 20% and with clean&distilled.

http://www.thelightfarm.com/Map/DryPlate/PlatePrep/DryPlatePart4.htm

Nodda Duma
27-Jan-2019, 13:22
For subbing layer:

Stir and melt 2g gelatin in 1L distilled water at 40C.
While the gelatin is melting, dissolve 2g chrome alum into 100ml water (2% solution).
Once the gelatin has fully melted into the 1L of water, add 10ml of the 2% chrome alum solution to this thin gelatin solution. Stir thoroughly.
Dip your thoroughly cleaned plates into this, drain, and allow to dry. Then you can coat your plates. The subbing solution is good for about 2-3 days, after whichbit is no good.

For emulsion hardening, just before coating, slowly add while stirring 5ml of the 2% chrome alum solution per 100ml of emulsion at 40C. Stir thoroughly. You have about 3 days to use up all that emulsion to coat plates with.

Pere Casals
27-Jan-2019, 14:37
For subbing layer

Thanks for posting this recipe, I've always coated directly on glass, but I'll try this way to see if I get less defects.

Nodda Duma
27-Jan-2019, 17:27
It will definitely help with frilling or lifting of emulsion if you do your part to clean the glass, and combined with hardening of the emulsion will eliminate temperature-related problems during development.

I run the solution through a gold mesh coffee filter before using to remove air bubbles and any particulates or unmelted pieces of gelatin. If you use it after cooling, add a shot of ethanol (vodka or everclear) to help reduce air bubbles.

Pere Casals
27-Jan-2019, 18:46
One question... if dipping the plate then the other side of the plate also takes gelatin... when do you remove it ?

Nodda Duma
27-Jan-2019, 19:50
One question... if dipping the plate then the other side of the plate also takes gelatin... when do you remove it ?

I don’t. At 0.2% gelatin, the resulting layer is so thin that there is no real need to. However, it can be removed after development along with any residual emulsion on the back side by using clorox wipes (or dilute bleach and a cloth).

Vaughn
27-Jan-2019, 23:30
Has anyone used potassium alum instead of chrome alum?

I've used it to clear/harden carbon prints.

Nodda Duma
28-Jan-2019, 03:15
You could use potassium alum as a hardener, but that doesn’t provide the advantage chromium does in bonding to the glass. So for glass substrates, historically chrome alum has always been used as the hardener.

Pere Casals
28-Jan-2019, 03:18
I don’t. At 0.2% gelatin, the resulting layer is so thin that there is no real need to. However, it can be removed after development along with any residual emulsion on the back side by using clorox wipes (or dilute bleach and a cloth).

OK, thanks !

I'll try it like you suggest, also I'll try to apply the preparation layer with a brush in the emulsion side only, it should work the same.

ruilourosa
28-Jan-2019, 04:18
i just promote some very gentle scrub with that cleaner that has some fisical abrasive content cif is the name, toothpast woud work too i suppose...

i

jnantz
28-Jan-2019, 04:44
hi OP
i used to sub layer with a hard coat of gelatin
but a handful of years ago, i just started coating
warm and putting on something super cold.
no hardener needed
and no sub coat needed. i was in total disbelief
when i was told it worked, and ... it does !

Randy Moe
28-Jan-2019, 08:36
Also informative!


hi OP
i used to sub layer with a hard coat of gelatin
but a handful of years ago, i just started coating
warm and putting on something super cold.
no hardener needed
and no sub coat needed. i was in total disbelief
when i was told it worked, and ... it does !

Robert Brazile
30-Jan-2019, 12:02
Jason has hard-earned experience that should be listened to, but for what it's worth, I don't sub. Just wash very carefully with detergent and water, more or less as Pere describes. For reused plates with stubborn spots, I use a bit of whiting in alcohol first.

Robert

Nodda Duma
30-Jan-2019, 18:46
Robert has a good point. I didn’t sub before I started selling them, but had to start doing so because other folks don’t or couldn’t control their temperatures as well, or had different water than what I use, etc.

jnantz
1-Feb-2019, 06:41
Robert has a good point. I didn’t sub before I started selling them, but had to start doing so because other folks don’t or couldn’t control their temperatures as well, or had different water than what I use, etc.

NoddaDuma
I forgot those things would keep an emulsion layer from staying stuck. > oops! < Your methods make it foolproof for someone to use dry plates. When I first learned I can't tell you how many layers swirled down the drain kind of like a polaroid-lift gone very bad.

Nodda Duma
1-Feb-2019, 06:56
To be perfectly honest the technical knowledge I’ve gained over the past year has been massive. It’s been such a great learning experience. I’m pretty happy to have gotten to the point where I can proudly say I know what I don’t know, rather than not even knowing that.

Randy Moe
1-Feb-2019, 07:06
Rebuilding the very secretive photography methods of the past is not easy

Deliberate misdirection was a common tactic to maintain superiority

aka Trade Secrets

I also admire your openness in process tips

You have done well!


To be perfectly honest the technical knowledge Iíve gained over the past year has been massive. Itís been such a great learning experience. Iím pretty happy to have gotten to the point where I can proudly say I know what I donít know, rather than not even knowing that.

jnantz
1-Feb-2019, 08:02
To be perfectly honest the technical knowledge I’ve gained over the past year has been massive. It’s been such a great learning experience. I’m pretty happy to have gotten to the point where I can proudly say I know what I don’t know, rather than not even knowing that.


I can only imagine ! For me the more I think I know the more I realize I don't know !


Rebuilding the very secretive photography methods of the past is not easy

Deliberate misdirection was a common tactic to maintain superiority

aka Trade Secrets

I also admire your openness in process tips

You have done well!


+1 !