Emulsion hardening

[iandvaag]

I'm having problems with a poorly hardened emulsion.

Yesterday I made a POP emulsion for TLF project. Today I printed and processed it, but it was pretty much a failure due to severe frilling and complete emulsion liftoff. I'm not doing anything like 30 mins of processing and 30 mins of washing. The process was:

1) Soak in tap water 1-2 mins to remove excess AgNO3
2) Pre-harden (10g/L formaldehyde, 100g/L sodium sulfate, pH ~9)
3) Fix (Ilford IF-2, pH ~4)
4) Wash

I've never made it to step 4, before then I have severe frilling and eventually complete liftoff. I've tried different times in the baths, but after about 5 mins of wet time, it falls apart. Processing trays maintained at 20C, I also tried at 0C (ice bath). It lasted longer, but ultimately didn't help.

Here's the sad mess I had when I was done:

I didn't add any hardener to the emulsion (I ran out of glyoxal, and I didn't think to use formaldehyde). I'm going to order some glyoxal and I will make sure to add it next time! Any other tips? I've often had problems with hardening in the past.

Has anybody tried the Rollei RBM52 hardener? The tech sheet claims it "is free of formaldehyde and chromium potassium sulfate due to a new formula and acts as a powerful hardener". Is it an aldehyde?

 

[Peter Schrager]

what is your substrate?? are you using watercolor paper?? how are you coating ?? what POP formula are you using??
I use fixed out Baryta paper to make prints. last summer I was having problems with frilling.
I was using a squeegee and mylar.
I don't have those problems anymore and have never used a hardener. is your running water very hot?? that could make a difference
I now use a Meyer rod for coating and will shortly try using a glass rod. I tape the paper to an oversized piece of glass. coat; let it set up and then hang it up to completely dry. with weights on the bottom to keep it from curling.
if the emulsion sets up quickly there should be no frilling at all and especially with watercolor paper.

 

[dwross]

I'll ditto Peter's questions. Frilling is not a problem I've experienced with POP. I did achieve complete emulsion lift-off once when I hardened dry plate emulsion with glyoxal. Tough, rubbery emulsion met a hard, smooth surface and away it went! I don't harden my dry plate emulsions any more. Hardener can be the problem as often as it is a solution. That said, please record every detail of what you're doing. The "mistakes" are at least as important as perfection when building a comprehensive narrative of a process . You'll figure it out. I'm very curious for the answer.

 

[iandvaag]

Thanks for your comments Peter and Denise.

I tried coating on 3 substrates:
Canson watercolor paper (140 lb, cold press)
Strathmore Smooth Bristol 300 series (100 lb, hot press)
cheapo Ucreate Paint Pad (90 lb)

All 3 had problems. What do you use for am inexpensive paper while doing tests?

I am coating with Ron's 4x5 blade gapped to 5 mil, and the coatings look good in the dark.

I had neither citric acid nor any citrate salt on hand (will be ordering shortly), and I didn't really want to go out shopping unnecessarily, so I made a formula from Walter Woodbury's The gelatino-chloride of silver printing-out process, page 78 attributed to Barker. It uses tartrate only and no citrate. I reduced the scale by a factor of 20 and adjusted for the salts I had available. I also didn't boil it as is suggested! Here's what I did:

A Bloom 8.75 g gelatin in 115 g water; raise temp to 40 C to dissolve. Add 1.25 g KCl. Add 1.67 g potassium bitartrate.

B Mix up 3.75 g AgNO3 in 10 mL water.

Add B to A over period of 1 minute at 50 C. Raise temp to 75 C over period of 10 mins. Filter and cool to 40 C. Coat at 40 C and dry.

My water can be very cold (~8 C), but I adjusted the temperature to 20 C (or 0 C for the last test) for each of the baths. I wasn't using running water for anything either; I filled a tray and gently placed the print in. I didn't even do any agitation, just to perturb it as minimally as possible, but it still didn't help.

I don't think the prehardening bath is causing problems since I initially tried the process without it, but the frilling started even earlier, after only about 2 minutes of wet time.

 

[dwross]

Ian. At first guess, I'd say your paper is the problem, or at least part of it. I've tried the Canson with other emulsions. The prints all had one odd problem after another. I gave my stash to the local elementary school art program. I have gotten big blisters on HP Bristol. The emulsion didn't lift off in a sheet like yours looks like, but still yuck. It was an emulsion with glyoxal in it.

My suggestion with paper is use good stuff, just be sure to make small prints. For example, one sheet of Arches watercolor paper (90 lb/ 185 gsm) is US$5.29 a sheet if you buy 5 or more sheets at Dick Blick. If you cut one sheet into three strips and coat with a 5 inch puddle pusher, you can get seven 4x5 pieces per strip, or 21 per sheet. That's a little over 25 cents a 4x5. A further suggestion is to initially buy one sheet of several papers and test with them to see which you prefer and then bulk buy that one. You'll pay a little more to start, but almost certainly save big money in the long run. One further suggestion: lighter weight paper is less expensive than the heavier versions of the same brand and work just as well, or better, than thick paper.

re Barker by way of Woodbury recipe: Below that recipe, Woodbury recommends a modification that adds alum and eliminates the alcohol. He may have had the same problems you've had with the recipe as originally written. Also, note that he specifies that the emulsion temperature should never rise above 120F. Either the Barker recipe had a typo (calling for 100C) or that high a temperature denatured the gelatin and contributed to problems with the recipe. You wisely avoided boiling your emulsion, but perhaps 75C is still too high. For what it's worth, I've never had much luck going over 55-60C with any emulsion recipe.

d

 

[iandvaag]

Thanks for the advice, Denise. Much appreciated.

Yeah, the Canson had other problems as you mention. I don't intend to use it again. I'll order some papers as you suggest; really I should have done more experimentation years ago.

Good points also about the Barker recipe and Woodbury modification. I had actually just intended to do a 10 min hold at 50 C, but I accidentally bumped the control knob on my hotplate, so I got a temperature ramp instead. Oops!

Thanks,
Ian

 

[M Carter]

if the emulsion sets up quickly there should be no frilling at all and especially with watercolor paper.

Maybe not 100% related, but I've found a great trick for fast setting - I coat on double thick glass; about the last ten minutes of heating the emulsion or gelatin, I dampen a bath towel and "hang" it in the freezer for ten minutes, and stuff it in a little lunch cooler. Ice cold but not frozen stiff.

Once I've coated the paper, I let it sit a minute or so while I put rods and spoons and stuff in the sink; then I spread out the towel on a flat surface (it's doubled up into 2 layers), and set the glass on it. The emulsion sets up very fast. I take a couple bondo squeegies and clear the set emulsion from around the paper, clip it to a thin aluminum bar with three clips on it, lift the bar and the sheet just gently peels right up, and even a 16x20 can't twist back onto itself; the emulsion is really pretty solid in minutes. I just hang the bar to dry. (I flatten the paper in a barely-warm dry mount press before printing).

 

[iandvaag]

Yikes, time flies! Sorry I didn't post back here sooner.

I tried again with the same formula, but being careful to maintain a temperature no greater than 50 C. I also added formaldehyde before coating, but I was met with the same result when I tried to process the paper -- severe frilling and reticulation. The problem occurred when taking the print out of the fix and into the wash. I tried prehardening, drastically reduced temperatures and several different fixers, but nothing was helping. I tried soaking the paper in several solutions of different pH (1, 4, 5, 6, 10, 12 made by mixing any of sodium bisulfate, acetic acid and NaOH), but there were problems in each case. The best result was: Rinse ~1 min, Fix in plain sodium thiosulfate ~3 min, and Wash in pH 1 solution with sodium bisulfate and acetic acid. This avoided the worst of the frilling and reticulation, but I did get large blisters.

I was always getting what looked to be good coatings in the dark, but upon close inspection in the daylight, I saw tiny crystals in the emulsion. I had been using potassium bitartrate instead of tartaric acid or sodium potassium tartrate. I looked up the solubilities again and potassium bitartrate is far less soluble than the other two. I'm quite sure it was dissolved when I started, but I guess it crystallized out upon drying. I think this did bad things to the integrity of the gelatin. To verify that this wasn't some other issue (gelatin, hardened, etc) I went back and made a basic azo-like emulsion and I had good success.

(Aside: I coated the azo emulsion on Strathmore Smooth and Fabriano Artistico Hot Press. The Fabriano has considerably rougher surface texture and is also sized better. It holds up to processing really well and is a joy to use, although it does curl a bit more. Typically on Strathmore, I can wash for 15 minutes before I start to get a small amount of liftoff near the edges. I don't have a print washer, just trays, and this is not enough of a wash as determined by a retained thiosulfate test. I never had any liftoff or frilling with the Fabriano, even after 30 mins of washing.)

So in conclusion, don't substitute Rochelle salt (sodium potassium tartrate) for cream of tartar (potassium bitartrate). Also, Fabriano is great and having a bit more tooth to the paper really helps with adhesion!

 

[Peter Schrager]

this morning I coated some fixed out baryta paper. I hung the paper to dry and several hours later I went to print on the paper.
I got massive frilling even in the first wash. What I'm proposing here is that the paper needs to set for a day or two.
I followed the above with some other sheets that I coated several days ago and had ZERO problems.
In my last emulsion I added 5ml of Glyoxal. seems to be working. I have seen a tiny bit of frilling on some prints but none on the primary print areas but todays prints had no frilling.
I'm going to pull out the paper I coated today and print on it tomorrow. I'm convinced the paper had not set properly; hence the frilling!

 

[Peter Schrager]

this is a follow up to my post yesterday
Emulsion needs to set. it is not enough for it to look hardened on the paper.
humidity will also affect the ability to harden. I have it on good hearsay that this paper was never made in the summer months because of humidity.
I hung up the sheets that I had coated which had frilling for several hours; ran the A/C hard and voila no frilling at all
A dehumidifier would probably help too but someone else will have to try that