View Full Version : Substrates for Shooting in Camera - FILM, Acetate, PET (polyester), Glass, etc.

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06-13-2012, 01:39 PM
Actually, the Melinex from the Formulary has an anti-static coating on the back side.

Regards - Jim

06-23-2012, 11:12 AM
This past week I ordered a tablet of 5 mil Graphix Dura-Lar sheets. Dura-lar (DL) is Graphix's brand of PET film. Last night I gave the DL an overnight soak in a 10% NaOH solution and I am happy to report that it worked at least as well as the PET cut out of the tomato container. Water beads like crazy on the untreated DL and spreads out and just sits nicely on the treated DL. Also, the DL did not become cloudy in it's overnight bath. Tonight, I plan to mix a batch of subbing solution and try subbing the DL.

Question about Subbing
When it is said that gelatin disperses in acid, does that mean that it doesn't gel? For example, if I swell gelatin and melt in 5% vinegar, it does not gel at room temperature anyway. That's what is meant by dispersion?

-- Jason

Photo Engineer
06-23-2012, 03:42 PM
The context of your question is unclear. However, you can melt gelatin in acid as well as water so you end up with gelatin in hot (or warm) acid or water depending on what you want. Gelatin will gel below 20 deg C or 68 F even in acid. However, extremely strong acid denatures gelatin and prohibits gelation. This gelatin is considered useless for most purposes as it can be easily washed away.


06-23-2012, 11:50 PM
Hi PE, patents and other literature regarding subbing discuss gelatin dispersing in weak acids. For example, from US Patent 2461475, Kaszuba et al:

Page 1, paragraph 2 (I'm editing this a little for brevity)

... Since hardened gelatin, as used for glass plates does not adhere to a film base, it is necessary to use a mixture of gelatin with an organic solvent for the material of the film base, such as acetone .... or an alcohol/acetone mixture. Gelatin is insoluble in these organic solvents and the film base is insoluble in water, but it is possible to prepare dispersions consisting of gelatin in a mixture of one of the organic solvents and water with a volatile organic acid, such as acetic acid ... as a dispersing agent.

The rest of this patent goes on to discuss the idea of using ascorbic acid rather than acetic acid as the dispersing agent. I recently reread this patent and I don't think I am clear in what they mean by dispersion. Since acid serves to desensitize an emulsion, what role is played by the acid? Why not just swell and melt gelatin in water, then add to an acetone and methanol mixture?

Typically an 8% or so gelatin - water mixture sitting on the shelf in my darkroom at room temperature (about 70F) will gel after a few hours. The gelatin - vinegar mixture does not.

By the way, the subbing solution discussed in the patent does actually work on CTA but its very finicky to make. If you aren't careful and have the methanol at the right temperature, you get a white, sticky glop in the bottom of your container.

-- Jason

06-24-2012, 12:25 AM
Results of first coating tests with PET are in. I coated NaOH prepared test strips (10% solution) from the veggie container PET and Dura-lar with an 8% gelatin with red food dye added. Other than the NaOH treatment, there was no additional subbing done.

Coating was simple, I just dipped the strips in the container of gelatin and made sure to coat both the treated and untreated part of the strip. This was straight gelatin - no hardener or anything. After drying, the strips were suspended in 68 F water for 10 minutes. Gelatin on the treated part of the strip stayed put. On the untreated part the gelatin showed frilling. (I would hazard a guess that gelatin on the treated part of the strip was holding it in place.) No observable red dye in the water.

This has been my standard test and showed failure of the PVC and acetate base in the past and success of the CTA, melinex and 3M films. If the gelatin stayed put on the PET, I have some confidence it will work.

Time to get more serious. If I have time tomorrow I think I will melt some emulsion and try this for real.

06-24-2012, 03:15 AM

How can this be so simple?

If the answer really is just to bath in some NaOH, then there is no reason for a hobbyist to try create corona treatment, or to buy ready-subbed materials more expensive and harder to find.

Well, it makes sense that this has not been described before; in an continuous industrial process, very long chemical soaks are not feasible. But for us and our sheets, it does not matter at all.

Now we only need a test with a real emulsion. Water beading test is the first step, coating gelatin with coloring and testing in water is a better one, but a silver gelatin emulsion may behave differently still. I had a case when I was testing acetate subbing formula that it worked for test coating with gelatin and color, "developed" in solution of sodium carbonate for 10 minutes or so, but it didn't work with real emulsion at all.

I have fingers crossed here that your test with real emulsion works. Good luck!

Photo Engineer
06-24-2012, 11:29 AM

The method described in the patent is one that has been known for years. Many authors such as Wall and Baker disclose subbing layers with gelatin in acetic acid and an organic solvent. If the gelatin does not fully dissolve, it can form a milky liquid which can be termed a dispersion. A dispersion is a mixture of a liquid and a solid, where the solid does not precipitate.


However, in photography, the terms dispersion and emulsion have become corrupt and are reversed and thus a dispersion may be an emulsion. It is hard to say.


These references are to the classic definitions of the two. If you reverse them then it is the photographic definition and this came about because the early workers either did not know what they had, or were not aware of the definitions.

In any event, I suspect you are discussing a classic mixture of two liquid materials which do not dissolve, and which form a single phase of one material with small droplets of the other material suspended in it. I will not use a classic term here due to possible confusion.

It is sufficient to say that this method has been used for over 100 years, and that Kaszuba must have claimed something unique.

I am glad that the Sodium Hydroxide method worked. Please take care as that solution is very strong and very dangerous. It could take the hide off of an elephant with no trouble at all. Use safety goggles when you use it and don't get any in your eyes.


06-24-2012, 01:07 PM
Now we only need a test with a real emulsion. Water beading test is the first step, coating gelatin with coloring and testing in water is a better one, but a silver gelatin emulsion may behave differently still. I had a case when I was testing acetate subbing formula that it worked for test coating with gelatin and color, "developed" in solution of sodium carbonate for 10 minutes or so, but it didn't work with real emulsion at all.

Yeah, been there, done that! I've got a full sheet of Dura-lar soaking now.

PE, you bet! I have no desire to lose my hide!

06-24-2012, 11:00 PM
Test #1 has given a mixed bag. For this test, I melted a small amount (10 ml) of emulsion and coated a test strip by dipping - same as the plain gelatin. After about 90 minutes drying at room temperature, a bath in stock XTOL for 10 minutes caused frilling. Now on the untreated part of the strip, the emulsion adherence was nil, on the treated part there was frilling but the emulsion in the center stayed firmly in place. I don't think the emulsion was fully dried and hardened yet.

Some other variables in the mix: 1) I forgot the hardener (3% chrome alum) again(!) and 2) the strip was rinsed in photo-flo water rather than just plain water prior to coating.

I have another strip coated and ready to test. The second one was only rinsed in plain water, was given a dip in a chrome alum bath for hardening and I plan to leave this one sit on my desk and fully harden overnight before testing.

Looking at the coating on the photo-flo rinsed vs non-photo-flo rinsed right after coating, I would say the strip not rinsed in photo-flo gave a nicer, more even coating. For now, I plan to avoid photo-flo and stick with plain water for future tests.

Photo Engineer
06-24-2012, 11:03 PM
Check for fogging in the coatings with the NaOH treatment. Strong base can affect emulsions.


06-25-2012, 07:11 PM
After getting home from work today I ran Test #2 which (if you are following the saga) is that test strip that got the hardener and no photo-flo rinse. Here was the protocol:

Ambient temp: 74 F
Development: 10 min stock XTOL
Wash/Stop: 1 min plain water
Fix: 5 min

Results: no frilling, no stripping and the gelatin in the treated area of the strip stayed put. Frilling was evident on the untreated part of the strip - which was to be expected. So now I have a controlled sample of one (lol) that has worked. Yay!

PE, I can't check for fogging on this one because this strip was coated in the light. It was just easier that way. I will check on the next one though. But the DMAX is fantastic! :p

Also, today, I ran across a relevant paper on prepping PET films doing a comparison of using NaOH and some sort of enzyme. Later tonight I will post either the paper or a link. It's from the fabric industry but the gist is that prepping PET in this way is a common practice.

-- Jason

PS: Has anyone tried to replicate my results?

Photo Engineer
06-25-2012, 07:46 PM

If the enzyme is takamine, be very very careful. We used this under virtual hazmat conditions at EK to dissolve gelatin.


06-25-2012, 08:57 PM
PE, that's not the enzyme. It's something else but I'm not going down that road anyway.

Here's a link to the paper I found http://dl.dropbox.com/u/4212013/Surface_structure_and_properties_Polymer_degradati on_and_stability.pdf

It's entitled Surface structure and properties of poly-(ethylene terephthalate) hydrolyzed by alkali and cutinase, written by Ilaria Donelli, Giuliano Freddi, Vincent A. Nierstrasz, Paola Taddei, and published in a journal called Polymer Degradation and Stability. Hopefully anyone interested can open the link. Let me know if it doesn't work.

Besides plenty of things I don't quite understand, there are two things of interest in this paper regarding the treatment of PET.

1) A treatment protocol is given,

For the alkaline treatment, PET films were immersed in a 1M NaOH aqueous solution at 40 C, for different times, from 30 min to 24 h, under agitation on a shaking bath (Isco SBH/D, 110 rpm/min). Afterwards, membranes were extensively washed with distilled water and dried at room temperature overnight.

So here they tell us the concentration of NaOH, temperature and process. I am making the assumption that since these fellows are associated with the fabric and dye industry, they are citing a standard method of processing.

2) The maximum necessary treatment time using the author's protocol is two hours,

Interestingly, both NaOH and cutinase (the ezyme being compared Ed) lead to a levelling of the WCA values which do not change too much for treatment times longer than 2 h.

WCA stands for water contact angle and refers to the amount of water beading displayed by the PET. The higher the WCA, the more beading. We want a low WCA.

I am treating a new piece of Dura-lar now according to the information from this paper and I'll report back when I get some new results.

-- Jason

Photo Engineer
06-25-2012, 10:11 PM
One Molar NaOH is 40 g/l. That is 4%. Very good luck to you. Looks good so far.


06-27-2012, 11:47 PM
Well, I'm back to write up some notes and observations. Maybe some of you can offer suggestions or at least it might help you to reproduce what I have done or go farther. A disclaimer here: I haven't yet used a 1M NaOH solution - the solution I'm using is 2.5M. Didn't have time to mix that up but it is on the docket. I did, however, run the current prep at about 100 F as mentioned in the paper cited above. I am running all tests right now with little bits of emulsion, but I am working on scaling up. My coating size right now would be about 6x7 cm. I have had two passing processing tests both after allowing the emulsion to harden overnight.

1) Hydrophilicity (if that's a word) of the PET is greatly increased. After the NaOH immersion and washing, I hang the sheet to dry. It literally takes an hour for the sheet of PET to dry.

2) Photo-Flo in the emulsion as a surfactant or in the PET wash (to avoid water spots - which probably doesn't matter) seems to be a disaster. Maybe the ingredients of the PF have a higher affinity for the PET than emulsion.

3) Adhesion when coating at room temperature (70F) is great until slitting the film. After slitting, when looking at the back side of the film, you can see where the emulsion has separated from the support. If you pick at it with a fingernail or x-acto knife, you can separate the support and emulsion. However, if you do not pick at it, the coating seems to pass the processing test. Using chrome alum as a coating time hardener (1 drop 10% CA in ~5 ml emulsion) seems to make no difference. I think this is a mechanical effect where the PET is more flexible than the emulsion. As an after-thought, I've had this same problem when coating 3M base at too low a temperature and I believe others have mentioned this as well. Denise gave me a coating temperature of 32.5C (~90F). I believe PE has mentioned 100F in the past.

Next actions:

a) Try coating with support at 90 - 100F. This ought to reduce the viscosity of the emulsion and make it easier for it to grab onto the micro-pores in the PET.

b) I have read in other postings about using ethanol as a surfactant. That's something else to try. QUESTION: Can IPA be used as a surfactant? I have lots of that. Everclear is NOT available in Pennsylvania but I am told I can use vodka.

c) a "lights out" coating and exposure in camera. If I can get a coating close to 6x9cm, I plan to expose it in my Kodak Tourist. It's 1940s lenses probably don't have the UV blocking properties of newer lenses (just guessing here) and I also think this would be the easiest camera to use, now that it is back in commission.

So some problems to work out but I've consistently gotten farther with the PET than other subbing methods I've tried. Oh, I also had a question of why not just use the 3M film or Melinex? Because I am looking for an inexpensive off-the-shelf solution and it's fun. :)

Stay tuned,

Photo Engineer
06-28-2012, 10:00 AM

IDK how you can coat at 70F. This is low enough for the gelatin to begin setting up. Usually, coatings are made at 100F. As for these coatings, the gelatin does indeed swell and shrink while the support does not do that very much. You can use alcohol instead of PF200, but you might try cutting down on the amount of PF. It is bad without but can be as bad with too much.

Why not use the Melinx? Because the mfgr wants a minimum order of 8 master rolls of full width and length. This would impoverish everyone but Bill Gates or someone like him!


06-28-2012, 12:04 PM
IDK how you can coat at 70F.

I am thinking that has been my problem with coating all along. Now the gelatin itself is around 100F. It's heated in a kitchen shot glass that has a thick glass base that stays nice and warm for several minutes after taking out of the water bath. But the support and the glass I am coating on is room temp.

The way I see it, the gelatin has got to be very fluid if it is going to flow into the micropores in the PET and grab onto it. Once the warm gelatin is poured onto the cooler base it would seem to me that a thin, high viscosity layer would form where the gelatin contacts the support and that would give poor adhesion. Make sense?

I've tried heat up the workshop/darkroom to a proper coating temp but cannot get above above 75 F or so unless I would start a bonfire. The support is taped to a 1/4" thick piece of glass. Can I heat that up with a hair dryer or something? Would that work? What do other people do?

I think I am missing something.

Photo Engineer
06-28-2012, 01:12 PM
Ok, I misunderstood. My darkroom is almost always at 70F and the plate I coat on is at ambient conditions or 70F. My melted emulsion and gelatin are at ~110F and my blade is at ~110F. I pour the emulsion or gelatin into the blade opening and coat. The mass of the blade maintains the melted material at above ambient conditions and the colder plate rapidly cools the substrate to about 70f. I then can hang it up to dry or leave it horizontal to dry.


07-02-2012, 01:55 PM
I just got caught up on all the progress here after being outta town for a while. Great stuff that keeps getting better.

I don't know if I'll be able to do any testing myself for a while, but in the future I definitely plan to. This appears to be a great discovery indeed!

Ok, now as per your question over here (http://www.apug.org/forums/forum205/107336-help-hardener-films-frilling.html), it seems clear that you need to have some kind of hardener in your emulsion if you want it to survive processing. Part of the workshop at GEH with Ron and Mark is to develop a coating that is unhardened and see what happens. Although my group didn't get around to doing, I understand that the result is an emulsion that nearly bubbles of the support, and that's on paper.

I understand that a silver emulsion might act differently, but part of my interest in a simple PET subbing procedure like this would be for the making of DCG-imbibition matrices. Until sensitized and exposed, these coatings would consist simply of gelatin/sugar/dye.

07-04-2012, 02:09 PM
Just a quick note about Grafix Dura-Lar Wet Media film. Last night I coated some sheets with 8.5% gelatin using both a 110-gapped Meyer rod and also a comb. So far, both coatings are sticking brilliantly to this surface.

I also took two sheets and washed them thoroughly under water, hoping to get rid of any kind of subbing layer. I plan to coat these and I hope to see the emulsion peel off cleanly when dry. I'll also do a much thicker coating of pigmented gelatin on my last good sheet and see how it goes.

But anyways, it's entirely possible that Grafix Dura-Lar Wet Media will work. Has anyone else had direct experience with this product? If so I'd love to hear your impressions.