View Full Version : Emulsion Stripping

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02-05-2012, 07:38 PM
Earlier today I PM'ed PE with the following and while he was good enough to answer, he suggested I post to the forums and so I am. Seems this has become general interest rather than a specific error on my part.


I was hoping maybe you could point me in a direction for some trouble shooting with an emulsion I have made. I'd post this but it's a pretty specific question.

I have coated the emulsion onto the film base twice (Grafix Clear-Lay 3 mil -advertised to be cellulose acetate) and both times the emulsion has stripped off the base after drying. The first time it just curled up and fell off. This second time the emulsion remained adhered to the film so much so that as the emulsion shrank as it dryed it pulled the base into wrinkles and curled. However, when I went to cut it down to the needed size it came right off the base as I cut it. Two different subbing formulas were used between the first and second attempt. Same batch of emulsion.

1st: Wall's 1929 formula
2nd: as described in US Patent 2461475 (Kaszuba-GAF 1946) using ascorbic acid. Example IV in the patent.

The second coating was made with the emulsion at a temp of 45C. Sorry, but I don't recall the first coating temp. The film base was taped to glass which I warmed over the water bath. The glass was warm to touch but I cannot say the exact temperature.

The subbing seems to adequately adhered to the base. I can wash the base in water and it doesn't seem to come off and there is a clear difference in how the water runs off the subbed and non-subbed areas of the base. The issue seems to be between the subbing and the emulsion.

Here's what I can think of as initial problems to investigate:

1) the subbing is left to dry too long (overnight in the first attempt)
2) the subbing is not left to dry long enough (One sheet coated after an hour second sheet coated after 10 minutes)
3) Coating at too low a temperature so the gelatin in the subbing has hardened
4) Something wrong in the emulsion make.

I am using the grafix film on Denise Ross' suggestion. I also tried her trick of coating some with a thinned gesso to practice and had no problems whatsoever. The emulsion is mixed according to her TLF2 recipe with 10 drops 10% w/v solution sodium thiosulfate added as a sensitizer.

As a side note, with regard to the emulsion itself, even though it stripped, it is strong enough to hold together so I taped it to a piece of the base and exposed in camera. Developing in XTOL for 6 minutes by inspection gave a visible negative. Exposure was made at 1/8 sec, f4, under today's bright sunshine. I'm guessing an ISO of about 4 - so the sensitization didn't seem to work.

Any suggestions or references you would have would be welcome. Sorry for my long note. I'm off to mix up a 10% gelatin solution and see if I can't figure out what my problem might be.

Thank you,
Jason Fox

**** And PE replied with....


I think that this question is worth posting but I will give and answer.

If emulsion strips off the support but remains as a cohesive film, then there is good hardening but poor adhesion to the support. With that understanding we can say it is one of two things, either the subbing is wrong, or the hardener is wrong. You don't mention the hardener, but generally aldehydes are used and in this case should probably work. Depends on the subbing. Wall has several formulas, one with Acetic Acid and Gelatin. In this case, the AA can inhibit (or accelerate) hardening depending on gelatin and pH.

I suggest costing between 100 - 110 F and using either glyoxal or chrome alum to harden coatings. If one will not work, the other usually does. Glyoxal takes about 4 hours to harden but CA takes up to 24 hours to harden. This includes interaction with the subbing layer.

Denise describes one of the acetates as having a subbing layer already. If so, double subbing can cause problems, but generally they are all minor and not like what you describe.

So, try changing hardeners first. If that does not work, get back to me.

Best wishes.

Ron Mowrey

***** And then I replied with the fact that I had forgotten the hardener and would have to try again..

-- Jason

02-05-2012, 07:39 PM
And then later from PE....


If you have good apparent hardness with no hardener present, that is a clue. Something is helping give your emulsion a cohesiveness it does not deserve. Of course, this might just be cold gelatin on a repelling substrate. To test this theory, dip a small piece of the stripped emulsion into warm water (75 - 95 deg F) and see if it dissolves. If it does, then it was cold gelatin coming off a repelling substrate. If it remains cohesive, then it appears that something hardened your gelatin while repelling it from the subbing layer.

Another clue!

02-05-2012, 07:40 PM
And now my reply to move this to the forum....

Thanks, PE. I'm going to move this to the forum and then reply when I figure something out. Right now I am just doing some trial and error with the 10% gelatin only mixture (no silver). Coating temperature of the substrate seems to have a lot to do with it because the warmer base coats better. Unfortunately, that isn't the whole problem because that will strip, too, if heated. Adding the hardener has also changed things because with hardener it seems to be harder to strip. (10% chrome alum added about .5 ml to 10 ml of 10% gelatin)

I'll also see about dipping some of the stripped emulsion into warm water.

-- Jason

Photo Engineer
02-05-2012, 08:08 PM
We will figure this one out. Don't worry.


02-05-2012, 08:56 PM
Oh, I'm thoroughly enjoying this! ;) So no worries here!

OK, between plays, seeing that the hardener seems to help, I made a coating with the hardened gelatin but modified the subbing to raise the acetone to approximately 30%. The subbing formula given in US Patent 2461475 (Kaszuba et al, GAF, 1946) "Gelatin Subbing Compositions Containing Ascorbic Acid (Vitamin C)" in Column 4 line 25 is:

Example IV
Gelatin 0.5
Water 1.3
Vitamin C 0.2
Ethanol 75.0
Acetone 23.0

Kaszuba says that examples IV and V can be substituted for any of the other formulas given. I found this formula interesting because I had ascorbic acid on hand and do not currently have glacial acetic acid. Also, I mispoke above about the base: the Graphix film is cellulose diacetate, not cellulose acetate.

Unfortunately this one also strips. I have a hunch that when the gelatin is drying (using moderate heat) the gelatin is shrinking and pulling the subbing away from the base because of the appearance of the diacetate where the subbing came off. To test this idea, I wet the stripped base and the area where the emulsion was applied is hydrophobic (the water runs right off - sort of like rain-x) and where the gelatin was not applied is still hydrophilic (as in it stays wet.)

Looks like the problem is caused by poor adhesion of the subbing to the base.

Also, a test of the earlier gelatin without hardener does dissolve in warm water. Since the actual emulsion has no hardener and strips in the same way I will presume that it, too, will dissolve.

Now that my glass is free, I will try to make a good quality coating with hardened gelatin. (My last with hardened gelatin was without the glass on a scrap of diacetate)

-- Jason

Photo Engineer
02-05-2012, 09:42 PM

I suspect (just a guess) that the subbing is not right for the support. If the subbing comes off as you indicate, then it isn't really adhering to the base which is the main purpose of a subbing layer.


02-06-2012, 07:36 AM
Well, that's because the base (Graphix Clear-Lay) is PVC, not cellulose diacetate. Last night, I cut a piece into very small pieces and put in a jar with straight acetone to soak overnight. Nothing happened. Acetate should have dissolved. A web search this morning shows that the material is actually PVC and not their acetate product. Looks like I ordered the wrong item or maybe "Clear Lay" used to be diacetate and changed to PVC. Thankfully, with plenty of school projects still to come I doubt it will go to waste. Maybe I can find a solvent for PVC? idk.

I will get some actual acetate, try this again and report back.

02-06-2012, 08:54 AM
I am watching this thread with great interest, as I have had my own struggles with coating 'film'.

IIRC, strong solutions of acetone (and most ketones) usually soften PVC. Perhaps there is some plasticizer or other additive in the product. I don't know if it's the case with Clear-Lay, but I've found that many plastics and papers benefit from a wash with water + surfactant to remove manufacturing residues (lubricants, powders etc., used to facilitate machine production, packaging), sometime a good puff of compressed air is enough.

I'm currently using fixed-out imagesetter film as a base material: it is very clear, dimensionally stable, and the subbing/emulsion layer is very tough.

Looking forward to hearing more about your adventures!

Photo Engineer
02-06-2012, 02:02 PM
I have a few feet of 4" wide (or thereabouts) acetate here somewhere. I usually use the Melinex from the Formulary, but I could check out the acetate or send a strip to you guys.


02-06-2012, 07:58 PM
I have some of the Grafix acetate product on order. They sell it in a pad of 9x12 sheets for about $9.00. From what I can tell, that ought to work. I also have a lead on some other pre-subbed material and looking forward to trying that, too.

For posterity, here is a scan of the negative I mentioned above:


Size is 35mm. This is only the emulsion smoothed out onto a microscope slide as best possible.

-- jason

02-07-2012, 01:54 PM
Yesterday afternoon, I spent some time researching solvents for PVC. Kaszuba gives an ascorbic acid subbing formula for PVC in the patent, above, mainly including a lot more acetone and less methanol, but I could not get it to work. Ian makes a good point that there might be some other coating or ingredient from the manufacturer. Grafix doesn't tell you what's in it in the MSDS.

Turns out PVC is pretty tough stuff but the main solvents are acetone, MEK and tetrahydrofuran. Acetone and MEK are weak solvents; the best, tetrahydrofuran. These solvents are also the ingredients of common PVC pipe glue along with a small amount of PVC resin. So, I tried adding a bit of PVC glue to the subbing formula. Unfortunately, this precipitates the gelatin in the subbing into a hard ball. Next attempt was to mix a solution of the glue with acetone and apply that mix to soften the PVC. If I apply this first dilute glue solution and let it dry, then apply the regular subbing, and then coat gelatin, the gelatin sticks very well and does not pull off the PVC.

The glue mix can do some nasty things to the PVC support so it appears that a very dilute solution is needed, since we just want to soften and not dissolve. The correct mix will likely be somewhere between 50:1 and 100:1 acetone to glue. The last attempt I made last evening was 30:1 and the PVC base is too optically distorted to be able to print from it. But the gelatin remained stuck firmly to the base.

02-12-2012, 09:21 AM
Last evening I had my first try of coating with the new 5 mil acetate. The subbing formula as given above works great and the gelatin "clings tenaciously" (as some of the patents say.) Now, last night I just did a run with practice gelatin (8%) but sometime here in the next few days will be some real emulsion. Here's hoping.

I am having some trouble getting the support to stay flat and not wrinkle so much. Subbing both sides helped but I'm not sure thats the answer. :confused:

Photo Engineer
02-12-2012, 10:23 AM
Well, we usually did not have problems with film support wrinkling, but if we did we used a vacuum hold down plate.

OTOH, we never had to suffer making our own subbing! ;)


02-12-2012, 11:27 AM
Back to the PVC.. have you considered (stabilised) chloroform?

02-12-2012, 11:53 AM
I am having some trouble getting the support to stay flat and not wrinkle so much. Subbing both sides helped but I'm not sure thats the answer. :confused:

Is this 'wrinking' occuring during coating, or during/after drying?

I've found that pinning my film base to a rigid support, or hanging with weighted clips helps keep things flat and smooth.

02-17-2012, 10:14 AM
Back to the PVC.. have you considered (stabilised) chloroform?

No, I didn't bother. I did find that reducing the amount of THF solvent (aka pipe glue) to a ratio in the 100:1 (acetone:glue) range helped to keep the PVC relatively clear. Since the PVC was a mistake by the purchasing department (me) I was anxious to move on when I received the acetate.

Is this 'wrinking' occuring during coating, or during/after drying?

The wrinkling was ocurring somewhat during coating the subbing but moreso during coating of the gelatin. Over the last few evenings I did a few more practice gelatin runs with 3 mil acetate rather than 5 mil on Denise's suggestion. There were a few issues I had to work out. I did find that in most cases the wrinkling would reduce as the gelatin dried.

One was temperature. Pouring out gelatin that was too warm on to room temperate acetate (fastened to the glass) caused wrinkling as the acetate would pull away from the glass.. Now, I was heating gelatin in the microwave and possibly making it too hot. So I switched to warming the gelatin in 15 ml batches a small stainless cup in 40C water. I also started warming the glass with warm air to about the same temperature. This made a big improvement.

Second was the amount of acetone in the subbing. For the diacetate film, less acetone seemed to do the job just as well without softening the diacetate as much. I had started with the acetone amounts called for by Wall or Kaszuba and reduced this down to about 25% of the original amount and the subbing still appears to work just as well. I haven't put any of this through a complete "processing" cycle but I don't see any difference in adhesion. I can roll it, bend it, twist it and the gelatin stays put. Maybe this is a difference between diacetate and triacetate, IDK.

Third was attaching the acetate to the glass prior to coating. I had simply been taping the acetate to the glass. That isn't what you want to do. (I did read somewhere about using a "stickyback" and moved in that directly.) What I worked out was to spread subbing on the glass, using a cotton ball or paper towel - either works, and then using a squeegee to work out the air bubbles and "glue" the acetate down to the glass. I start at one end of the acetate and glue down about a third of it and then do the rest, working the bubbles out along the way. My squeegee is a windshield wiper glued to a wood block, but I guess you could use anything.

Once the acetate is stuck to the glass, sub the top surface and let that dry for a minute or so to let alcohol and acetone evaporate. Then tape down the edges of the actate to keep it in place. The acetone and alcohol in the subbing solution will dissolve the tape (at least the tape I am using) if you try to tape it before applying subbing. It makes a mess.

One variation on the above I tried to apply the subbing was to spread subbing over the acatate and then use the squeegee to remove any excess. this leaves a really nice looking piece of acetate ready to coat and adhesion seems to be good. Unfortunately the subbing solution attacks the rubber winshield wiper. In the end there didn't seem to be any real difference once coated with gelatin. IDK if I will end up with subbing lines or not.

After getting this worked out last night, I set up one final piece of acetate and coated some real emulsion. Although I think my coating is too thin (unrelated problem - I had figured this wet coating to be about 8 mils but 12 seems to work better) it adhered nicely to the base. After drying overnight, it remained stuck to the base and looks pretty good. It'll be cut up and go in the camera today or tomorrow.

Denise also sent me a quantity of the pre-subbed melinex and I will be trying that as well. While I am sure the factory subbed stuff will be very nice, I want to be able to "own the whole process" just for fun.

Lastly, for what it's worth, the little stainless cups I mentioned above that I am using to heat gelatin, which I also use to hold weighed and measured chemicals, etc, come from the kitchen gadget section of Walmart. They are stainless condiment holders and you can buy a package of 4 IIRC for 88 cents. They hold about 35 ml. Work great!

02-18-2012, 01:46 PM
Tried out the film today. Everything worked up through the developing part. Then emulsion floated off the base in one piece by the time I got to the fixer. Starting to feel like Thomas Edison with light bulbs! I now know about 26 ways that don't work. :p

Photo Engineer
02-18-2012, 01:51 PM
This is an adhesion problem then not a hardening problem.

It is not clear whether the subbing or the emulsion is separating though. Not enough information.

Either way, I don't have a clear solution for you except to say try a different hardener in your gelatin.


02-18-2012, 01:53 PM
How could I tell if it is the emulsion or subbing?

Two things I will try to proceed:
1) I will restore the acetone back to the original levels now that I have a better coating workflow and make some more practice runs but now include soaking in some water to simulate processing.
2) Coat some of the pre-subbed melinex and see how that performs.

Photo Engineer
02-18-2012, 02:12 PM
Several thoughs:

1. What hardener and at what level did you use it.

2. To see if it is the emulsion + subbing stripping off, you will probably seen a tacky layer on the back side of the emulsion. If there is one, then the emulsion and subbing probably left the support. If there is no tacky layer on the film, then probably both the subbing and emulsion floated away or the subbing stayed in place and the emulsion floated away. Then check the film to see if it has a tacky layer of subbing.

In the case of emulsion + subbing leaving then there is no real adhesion of the subbing. It is the wrong subbing for the film support. If the subbing stays and the emulsion leaves then there is no adhesion of the two and the subbing is wrong for the emulsion.

The one common cure is a different hardener as I said earlier, or a much higher level. Or, you are not letting the coating cure long enough!