Blisters or bubbles in home made paper emulsion

Cor · Mar 31, 2025

Dear all,

I am making my own emulsion for a chlorobromide enlarging paper with reasonable success. I coat on Simili Japon paper and have this problem with bubbles or blisters in the fixer or sometimes in the wash as well

see also: https://www.photrio.com/forum/threads/emulsion-bubbling-during-processing.158633/

I do not have this problem as massive as above post: sometimes 1 or 2 on a 10*15 cm print (diameter 2-4 mm or so) sometimes none. The late and missed PE mentioned the use of a hardener when making the emulsion. I use no hardener now, any suggestions ?

My workflow is using the same chemistry as I use for standard factory silver gelatin. Including an acid stop bath.

Should a short rinse in plain water after the acid stop and before the fixer help ?

And after development keeping the print upside down so the CO2 can escape through the back ? (at the risk of damaging the emulsion through the tray perhaps?)

Any suggestions appreciated !

best,

Cor

koraks · Mar 31, 2025

We've discussed this and of course I can't offer good advice based on silver-gelatin experience...having said that, this appears to be a problem of adhesion, which brings to mind a couple of things:

* As I understand you're working with Simili Japon, which is a hot-pressed, smooth-surfaced paper. This has little 'tooth' to it that a gelatin emulsion can adhere to. You might get better results (although at the cost of fine detail rendering) by trying a paper that has a slightly more rough surface.

* To resolve the adhesion problem, you could try preparing the paper so it more readily accepts a relatively thick gelatin layer. In other words - applying some external sizing. You could dip the paper in a weak gelatin solution (let's say 1% or so), the let dry. Maybe harden that sizing as well. Then apply the image-forming emulsion. I'm pretty confident you'll have perfect adhesion in that case. But it adds another step.

* I'm with PE on the issue of a hardener and as I recall this was also what I suggested when we met last time in Amsterdam; I was actually surprised (hence my question) you weren't using a hardener. I'd certainly give it a try on one batch.

Interesting thoughts about the CO2; yes, who knows this plays a role. Come to think of it, Simili Japon is a buffered paper, so once you dunk it into an acid stop bath, maybe CO2 becomes a problem in the actual paper base as well? IDK, just a bit of a guess, really. I doubt there's a good way to force the CO2 to escape through the back of the print; if anything, I'd opt for the opposite and try to get it to escape from the emulsion instead of finding its way between the emulsion and the paper base. Moreover, I don't think placing the print upside down will actually force any bubbles to the other side. Gravity doesn't pose enough of a force for this.

Daniel Stuefer · Mar 31, 2025

While I have not (yet) coated and processed any paper, with glass plates I have noticed that increasing the gelatin percentage (weight) improves adhesion to the glass plates, so you could also try adding more gelatin. I believe my emulsions are usually around 15% (weight) 280 bloom gelatin.

Using harder gelatin might also work.

Cor · Mar 31, 2025

Daniel Stuefer said:
While I have not (yet) coated and processed any paper, with glass plates I have noticed that increasing the gelatin percentage (weight) improves adhesion to the glass plates, so you could also try adding more gelatin. I believe my emulsions are usually around 15% (weight) 280 bloom gelatin.

Using harder gelatin might also work.

I use Bloom 300 gelatin (porcine Type A), not for photography, at 10% the ADOX gelatin for emulsion making gave me background, and the one I am using now is completely clear in the non exposed areas. As I understand it : gelatin is also an important component in the sensitivity, why I do not want to mess to much with it. And I wet coat with a coating rod, finally got that step smooth and reproducible. I assume that a higher percentage will also influence my coating.

Cor · Mar 31, 2025

koraks said:
We've discussed this and of course I can't offer good advice based on silver-gelatin experience...having said that, this appears to be a problem of adhesion, which brings to mind a couple of things:

* As I understand you're working with Simili Japon, which is a hot-pressed, smooth-surfaced paper. This has little 'tooth' to it that a gelatin emulsion can adhere to. You might get better results (although at the cost of fine detail rendering) by trying a paper that has a slightly more rough surface.

* To resolve the adhesion problem, you could try preparing the paper so it more readily accepts a relatively thick gelatin layer. In other words - applying some external sizing. You could dip the paper in a weak gelatin solution (let's say 1% or so), the let dry. Maybe harden that sizing as well. Then apply the image-forming emulsion. I'm pretty confident you'll have perfect adhesion in that case. But it adds another step.

* I'm with PE on the issue of a hardener and as I recall this was also what I suggested when we met last time in Amsterdam; I was actually surprised (hence my question) you weren't using a hardener. I'd certainly give it a try on one batch.

Interesting thoughts about the CO2; yes, who knows this plays a role. Come to think of it, Simili Japon is a buffered paper, so once you dunk it into an acid stop bath, maybe CO2 becomes a problem in the actual paper base as well? IDK, just a bit of a guess, really. I doubt there's a good way to force the CO2 to escape through the back of the print; if anything, I'd opt for the opposite and try to get it to escape from the emulsion instead of finding its way between the emulsion and the paper base. Moreover, I don't think placing the print upside down will actually force any bubbles to the other side. Gravity doesn't pose enough of a force for this.

Thanks for the suggestions. I should add that I started out with the FOMA emulsion without the hardener added (foolishly I cannot find that small bottle anymore), using the same workflow on Simili Japon, and had no blisters. Guessing that there is already 9soem) hardener in the FOMA emulsion to start with.

Is it know what exactly the FOMA hardener is ? Or any other hardener recipe which I could add to my emulsion making ?

thanks,

Best,

Cor

koraks · Mar 31, 2025

I don't think there's any hardener in the foma emulsion, as it would make repeated melting impossible. It's possible however that the gelatin is simply different, and/or any surfactants used.

For a hardener, I suppose anything should work, ranging from chrome alum to formalin, glyoxal, glutaraldehyde etc. I'd personally start with chrome alum because it works quite fast, it can be 'dialed in' to the desired degree of hardening and it shouldn't upset the pH too much.

Daniel Stuefer · Mar 31, 2025

Cor said:
I use Bloom 300 gelatin (porcine Type A), not for photography, at 10% the ADOX gelatin for emulsion making gave me background, and the one I am using now is completely clear in the non exposed areas. As I understand it : gelatin is also an important component in the sensitivity, why I do not want to mess to much with it. And I wet coat with a coating rod, finally got that step smooth and reproducible. I assume that a higher percentage will also influence my coating.

Yes, gelatin does affect speed: if more is added to the initial make (before ripening), it slows down crystal growth. If you were to add more gelatin after ripening, it does not affect growth in any way, and should have a minimal effect on emulsion speed.

Some reagents in the (active) gelatin (some sort of sulfides I believe) increase speed in a different way ("sulphur sensitisation"), in photo gelatin this is always removed.

Lachlan Young · Mar 31, 2025

Cor said:
know what exactly the FOMA hardener is

Chrome Alum from the MSDS I recall. It can take a little bit of time to reach maximum hardening.

Ron's book has a range of hardeners, ranked by effective hardening vs relative toxicity. Glyoxal was the one he seemed to recommend most.

If your processing chemicals are relatively cold, you might largely get away with things without hardening - though a hardening fix (or stop bath if you are so inclined) can also help.

Cor said:
And after development keeping the print upside down so the CO2 can escape through the back

Not going to prevent damage, it's from a reaction inside the emulsion layer. Hardening is the solution.

koraks said:
As I understand you're working with Simili Japon, which is a hot-pressed, smooth-surfaced paper

Not really an issue, silver gel sticks to most of those sort of HP substrates very well - the paper in question is surface sized with starch too. If it sticks to baryta, it'll stick to HP finishes.

koraks · Mar 31, 2025

Lachlan Young said:
silver gel sticks to most of those sort of HP substrates very well

Apparently, it doesn't in this case. Btw, I have used this paper a lot for various purposes. I'm quite familiar with it.

Lachlan Young · Mar 31, 2025

koraks said:
Apparently, it doesn't in this case. Btw, I have used this paper a lot for various purposes. I'm quite familiar with it.

Ah, if that's the stuff that was supposed to resemble a Japanese paper (imitation parchment really), then I can see why - the surface permeability will likely be somewhat low, performing a bit closer to a coated offset stock (i.e. drying by evaporation alone, vs drying by absorption and evaporation). Ron does recommend HP papers in his book, though now that I think about it, the ones I've used were/are gel sized (tub sized) - or not necessarily surface sized - and for 'proper' Japanese papers, I've had startlingly good results with the inkjet receiver coated Awagami papers (just be very careful with the amount of emulsion you apply - Ron's comments about coating singleweight and lighter paper being like dealing with wet paper towel are amply illustrated). Chill setting the emulsion immediately after coating and before drying also helps with adhesion

koraks · Apr 1, 2025

@Lachlan Young it is this paper: https://www.polymetaal.nl/contents/...apon-225-gr-48x64-cm-tube-with-10-sheets.html
I recognize what you say bout this feeling a bit like a coated offset stock. Technically, that's not what it is, but one of the surfaces does feel that way a bit. The backside is a little more coarse and might in fact accept a gelatin layer a little more easily, but I think @Cor is using the smoother side as the image side. I've had the pleasure of seeing a couple of his (very nice!) prints in person.

Cor · Apr 1, 2025

I started out coating the rough side of Simili Japon (well rough is relative here) thinking better adherence of the gelatin and than I noticed the blisters forming. Switched to the smooth side and that seemed to help, but this is purely n=1, did not do any thorough testing, it is quite laborious as you all know. I am not overfly bothered by the blisters, it is hand work at all, but it would be nice to reduce or get rid of them. Next time I will do some testing with chrome alum. I suppose you add it after the ripening phase, when you cool down the emulsion and add an emulsifier (I use PhotFlo). Any hints on a starting concentration of chrome alum ?

Actually I am more bothered by the lack of contrast in my prints, I seem to reach roughly a grade of 1 1/2-2 at most, but perhaps that is better discussed in a different post.

thanks all,

Cor

koraks · Apr 1, 2025

Cor said:
I suppose you add it after the ripening phase, when you cool down the emulsion and add an emulsifier (I use PhotFlo). Any hints on a starting concentration of chrome alum ?

I'd add the hardener immediately before coating and only to the volume you'll use to coat a single sheet. The reason is that once you add the alum, the crosslinking process starts immediately. Depending on how much alum you add, you'll notice coagulation to commence immediately or after 10-20 minutes. There's a large bandwidth here, but either way, you'll find that once the hardener is added, the clock starts ticking and there's not much time set on it.

Peter Schrager · Apr 1, 2025

Cor said:
I started out coating the rough side of Simili Japon (well rough is relative here) thinking better adherence of the gelatin and than I noticed the blisters forming. Switched to the smooth side and that seemed to help, but this is purely n=1, did not do any thorough testing, it is quite laborious as you all know. I am not overfly bothered by the blisters, it is hand work at all, but it would be nice to reduce or get rid of them. Next time I will do some testing with chrome alum. I suppose you add it after the ripening phase, when you cool down the emulsion and add an emulsifier (I use PhotFlo). Any hints on a starting concentration of chrome alum ?

Actually I am more bothered by the lack of contrast in my prints, I seem to reach roughly a grade of 1 1/2-2 at most, but perhaps that is better discussed in a different post.

thanks all,

Cor

contrast related: you might want to try double coating which is what I do with my POP emulsion

Cor · Apr 1, 2025

Peter Schrager said:
contrast related: you might want to try double coating which is what I do with my POP emulsion

I already increased the thickness of my coat which helped with the Dmax, it is more that I want my whites more white, ie a stronger contrast so instead of 1 1/2 to 2 1/2 or so

best,

Cor

Peter Schrager · Apr 1, 2025

Cor said:
I already increased the thickness of my coat which helped with the Dmax, it is more that I want my whites more white, ie a stronger contrast so instead of 1 1/2 to 2 1/2 or so

best,

Cor

thickness of the coating is not what I think will increase dmax.....
I coat; let dry and coat again...voila more dmax!

koraks · Apr 1, 2025

Peter Schrager said:
thickness of the coating is not what I think will increase dmax.....

That's odd, because it does work that way with other colloid-based processes where the colorant/pigment is embedded in a colloid. Thicker layer = more density. In fact, with processes like carbon transfer, it's the heart of the mechanism. I'm quite sure it works that way with silver gel just as well, although it's debatable what the best way of making a thicker layer is. Whether this is multiple coating passes or applying a single, heavier layer.

Lachlan Young · Apr 1, 2025

koraks said:
The backside is a little more coarse and might in fact accept a gelatin layer a little more easily

I've encountered a few other similarly smooth surface stocks - Zerkall did one that was marketed to wood engravers.

I think it's really a question of surface (micro)porosity rather than texture - it's something I've run up against in other ways with ink-on-paper processes (especially with surface sizing designed for good hold-out) - which is also likely relative to the amount of wet-loading you are subjecting the surface to (a lot more with silver-gel than platinum for example) - and thus surfactant/ hardening/ coated layer thickness on first pass/ chill-setting choices become much more critical.

Cor said:
Actually I am more bothered by the lack of contrast in my prints, I seem to reach roughly a grade of 1 1/2-2 at most, but perhaps that is better discussed in a different post.

If it's an enlarging speed emulsion, it's probably more to do with the limitations of the fundamental crystal habit of the emulsion - a very high chloride percentage contact speed emulsion has an inherently much more desirably monodisperse crystal habit (and thus much better covering power for a given layer thickness) - and a huge amount of emulsion research was seemingly effectively dedicated to getting AgCl crystal habits out of AgClBrI emulsions to make harder grades at enlarging speed a functional reality. You might simply be hitting the limits of what you can achieve without having to introduce means to create a more controllably monodisperse emulsion. Getting G2 is pretty good going - a great many mid 20th Century enlarging emulsions maxed out at a hard G3 if they were lucky. A good part of Agfa's mythos was built around them getting Brovira to what we know as G5 quite a long time before anyone else did.

What PhotoFlo are you using? The 200 & 600 (the Kodak Pathe Photo Flo was 600, despite not being named on the bottle) does/ did have a component that can act as an emulsion accelerator - and it is used as such in a number of Ron Mowrey's emulsion recipes to adjust contrast, along with KI and antifoggants. {Moderator note: further discussion on the topic of accelerators can be found here: https://www.photrio.com/forum/threads/emulsion-development-accelerators-in-surfactants.212974/}

Cor · Apr 2, 2025

On PhotoFlo; I first tried Amaloco wetting agent H10, do not know what is in there, company is gone, but I was starting up trying al sorts of things it did not seem to help, left it out.

I moved on, mainly working with the FOMA emulsion, but I had recurring problems with uneven coating (I wet coat, use a coating rod with small pieces of tape at the ends, creating a slit), a kind of stutter because I could not maintain an even speed with the rod due to friction.

When I finished the FOMA I went back to home made, and per Denise Ross I included PhotoFlo.

Since I did not have the original stuff I made it myself: 2.75 g propylene glycol, 750 µl TritonX100 in end volume of 10 ml (this is assumed to be 50% working strength compared to the Kodak stuff)

Now my coating is quite smooth.

best,

Cor

Cor · Apr 2, 2025

And back to the blister subject (other posts have been very helpful, thanks for that !)

last night I finished my last 4 sheets, and no blisters !

What I did:

I coated 7 sheets of 18*24 Simili Japon (effective area about ~11* ~22 cm, 6 ml emulsion) that is about the max I can produce in my tiny workspace, coating takes me 30-40 minutes and I am always worried if there is a difference between the first and last sheet. Actually the last sheet was badly coated.
3 days later I printed on 3 sheets and got 1-2 blisters on 2 sheets, none on the third.
Last night (5 days after coating) I printed the last 4 sheets, and I used a more energetic developer; home mixed D19 (for Xray film) using straight for 2 1/2 minutes.
D19 helped to boost the contrast 1/2 a grade (maybe even 1 , I did not print step wedges), happy about that, but at the expense of a light veil in the unexposed parts, which I do not see with my normal developer.
I put the developed print up side down in the stop bath (when processing Cyanotype on Simili japon, and clearing them in the acid bath I see bubbles appearing on the back side of the paper, so I tried this in the regular stopbath as well, did not see bubbles though)

So no blisters, but is this because of the D19, the upside down in the stopbath, or perhaps the longer time since the coating (some kind of auto hardening?)

best,

Cor

koraks · Apr 2, 2025

Cor said:
So no blisters, but is this because of the D19, the upside down in the stopbath, or perhaps the longer time since the coating (some kind of auto hardening?)

My guess is that the upside down stop bath doesn't do much, and if it does, it's just a marginal workaround to cover up a more fundamental problem.
Hardening does progress over time. If you added e.g. chrome alum hardener to your emulsion, then yes, it can definitely take several days or weeks until the degree of hardening 'flattens out'(I think it asymptotically approximates a limit value; the rate and limit value depend on the type and concentration of hardener, mostly).
The D19 may have helped some if this also involved a shorter development time, but that's not clear from your story. Btw, 2.5 minutes sounds kind of long. With regular FB and RC paper, my standard development time is 1 minute, sometimes 1.5. I just mix the developer strong enough to get the job done within that time. A shorter development time can help in your case as it reduces the time in the alkaline bath which is the most risky part w.r.t. gelatin stability.

Cor · Apr 2, 2025

I agree that upside down in the stop bath is probably wishful thinking, and shorter in D19 is certainly on my list, the image came up quick. I did not venture into adding hardener yet, it sure would be nice if the D19 solve the blisters (but why? if anything it is more aggressive) and increase the contrast.

best,

Cor

koraks · Apr 2, 2025

What's your normal paper developer? It's hard to tell whether D19 is more aggressive without knowing the benchmark. My rationale is that a more active developer is not necessarily more aggressive for the gelatin (or its adhesion). For instance, you might have a relatively low-pH developer with a high content of developing agents compared to a high-pH developer with a low concentration, in which the latter might be less active but more aggressive towards the gelatin as such.

As to hardener - if you haven't used any, then I wouldn't expect your emulsion to harden much at all after it dries out after pouring. But maybe there's a slight effect over the first few days; this is possible. I do notice with carbon transfers that before the developed image matrix has dried it, it's very sensitive to disturbance (e.g. permanganate clearing etc), whereas once it has dried out, it becomes very rugged. I can imagine something similar happen to silver gel emulsion in the first days after pouring, as the moisture content is settling towards equilibrium. But this is all a pretty wild guess.

Lachlan Young · Apr 2, 2025

koraks said:
Btw, 2.5 minutes sounds kind of long.

Seconded - that's a very long dev time for a handcoated, non supercoated emulsion - in fact, I think the fogging that @Cor is seeing probably is general fogging from excessive developing time - a minute is usually plenty even at normal working strength.

koraks said:
I can imagine something similar happen to silver gel emulsion in the first days after pouring, as the moisture content is settling towards equilibrium.

There are some interesting complexities in the handling of coated, unhardened emulsions - Shanebrook has some references to how it was tackled industrially.

Quickly summing up Ron's segment on hardeners, he categorises as following:

Formaldehyde - Very Toxic - Fast Hardener
Glyoxal - Mild Toxicity - Medium Hardener
Succinaldehyde - Very Toxic - Medium Hardener
Glutaraldehyde - Very Toxic - Medium Hardener
Chrome Alum - Toxic - Slow Hardener
Vinyl Ethers (BVSME) - EXTREMELY TOXIC (caps as per original) - very fast, modern hardener, needs special handling in manufacturing (it's so fast reacting that traditional melt & coat methods would cause it to harden en route to the coating head), but safe for the end user of the hardened, coated product.

He states that the Aldehydes may take up to a year to fully react (but are sufficiently hard for processing paper coatings after "about 4 hours") and that Chrome Alum can be so slow acting that some emulsions were made with it already incorporated (i.e. would not gum up the coater). His recommendation of Glyoxal was based off it having a lower vapour pressure than the other aldehydes. I've not had many major issues with Chrome Alum hardening, even after quite short (hour or so) intervals after coating/ drying before processing.

Raghu Kuvempunagar · Apr 2, 2025

Acidic stop bath and acidic fix. Could some thiosulphate be decomposing in the emulsion due to acidic conditions and releasing Sulphur Dioxide bubbles? Thiosulphate decomposition generally requires stronger acid but who knows.

Blisters or bubbles in home made paper emulsion

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