Jon, could be the glutaraldehyde as well -> if that's Ryuji's stuff, there should be a weak alkaline buffer in it (for preservation)... (IIRC!) But, on the other hand, since the hardener's alkalinity is weak and it's used in very small amounts, probably it's more about the gum - as you assume. (Gum can be very different batch to batch / supplier to supplier...)
Originally Posted by Jon Harwood
yes, I know them (fisheyes). Had them also, but so far I have always been able to finally coat such areas.
Loris, 10cc household ammonia (9%) for 0.8g casein is my ratio. 12-30 drops for an 8x10, depending on paper, contrast, pigment, and so on, about 1.5cc dichromate (I mostly use 6% or 10% potassium, ammonium for soft contrast, sodium for some reason I have so far mostly used for gum), and I regularly regularly give a first coat of only casein and water (15-25 drops for an 8x10).
The casein image is more stable than gum, I most of the time end up developing some areas by dropping water on then, only rarely brush for small detail. A disadvantage is that the casein image stops dissolving/developing after some time, so your exposure needs to be more on the spot.
I tried with 25% ammonia (d=0.91g/ml): 1.6g casein + 10ml water + 12 drops of ammonia (~0.5ml) + water to make 20ml + 2ml isopropanol (to eliminate bubbles) gave me a pretty homogeneous solution. The amnt. of ammonia I used was approximately 0.0625g per 0.8g casein; that is ~14-15 times weaker than your formula! Should I definitely add that much ammonia? (Or, the criterion is to have a homogeneous "solution"?) Is there a strict/dictated amnt. of ammonia?
Not at all, or not that I would know. I arrived at my ratio entirely through trial and error. It has a strong smell of ammonia (the dichromate turns yellow), but I can dissolve the ammonia quickly in this way. I find this wishful because the solution, as far as my trials go, has very poor keeping qualities, even in a fridge. I make only 10-20cc at a time, depending on my need, and use it within 24 hours.
Originally Posted by Loris Medici
I have kept the ratio simply because in this way I get a handle on how many drops of casein solution I need for a given coating.
A different voice
Jon, I'm curious how much time elapsed between printing on glyoxal with the old gum and printing on glutaraldehyde with the new gum, and whether the seasons/weather changed between. My own experience/observations don't support the idea that either gelatin hardeners or different gum brands could make that much difference in speed. A difference, sure, but when I tested six different gums, the biggest differences between them were more like an exposure increase of 1/3 or 1/4 (in other words, an extra minute on an average 3 or 4 minute exposure) nothing like one gum needing 3x the exposure of another, so I am inclined to be very skeptical about this explanation. And by the same token, I've seen similar small variations in speed between different sizings, but not huge variations like this. But, I have seen, routinely, huge differences in speed when seasons change, particularly when there's a marked change in ambient humidity, so that's my first thought. Often it's not the obvious culprit, but something else, that's causing an effect.
BTW, I would caution anyone thinking of using glutaraldehyde to be sure to buy only the very dilute solutions now available from some supply houses especially for this purpose (like Bostick and Sullivan or Photographers' Formulary). Under NO circumstances should you buy it from a chemical house and dilute it down yourself, unless you have access to a lab with a vented hood. I started with 8% and breathed too much of it while diluting it, even though taking care that there was good air circulation, with rather disastrous results.
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It has been a very odd occurance. The time elapsed between glyoxal sized paper and glutaraldehyde sized paper was one day. Prior to printing I test the humidity with a sling psychrometer and there was no change beyond the 10% range. Temperature and weather were similar.
However I had recently been bedeviled with a series of difficulties. First, about a week before switching sizing I was confronted with severe fisheyes on the second tricolor coat. I attenuated this problem by pre humidifying the paper prior to coating. ***This pre-humidification may have reduced the exposure times.*** The pre-humidification helped with the fisheyes, but then I got a staining problem, so I double coated some paper using glyoxal and was able to print, I also continued to pre humidify the paper before coating. The double coated paper still had a stubborn problem with fisheyes even though I could brush them out when the paper was pre humidified .
Then the glutaraldehyde arrived from photographer's formulary and I single coated some paper with it. Simultaneously my gum supply from photographer's formulary kits ran out and I opened a new 1/2 gallon bottle of photographer's formulary gum. I printed with the new gum, the new sizing and I did not pre-humidify the paper (I had forgotten to say I was not pre humidifying the glutaraldahyce sized paper in the earlier post) This was the point at which the required exposure seemed to triple. The fisheyes were much less of a problem and I could brush them out during coating. As I have continued printing with the new sizing I am also thinking the increase in exposure may have only been a factor of two (one stop) not three.
At present I think the increase in exposure may have been caused by mostly by switching away from pre humidified paper and possibly by getting a different batch of gum that may be either younger or older than the prior batch. The change in sizing may have also contributed but I think the most important thing could be discontinuing the pre humidification step.
What ever the cause it has been one in a series of strange problems I have had to figure out. I have found myself quite totally hooked by gum even though it seems to be doing anything and everything it can to convince me that it is impossible to handle. After the last batch of challenges I seem to have arrived at a workflow that is producing one or two steps of extra contrast and which holds out hope of making a tricolor in three steps rather than five or six, so it has probably been worth it.
BTW I am very paranoid about glutaraldehyde. I handle it as if it was formaldehyde using particular caution when diluting it from 24% to 02.4% in a well ventilated area. I do not appear to be sensitive to it under the conditions I used it.
Thanks for the advice and analysis it reminded me of what may well have been the decisive factor.
Originally Posted by Katharine Thayer
regarding the problems of glutaraldehyde you mention, I am curious about its advantages. Do you think it is better than glyoxal (or,l for that matter, formaldehyd), and, if yes, why?
Also, can it be brushed on in an extra step? This is what I usually do with my glyoxal.
Jon, that's a serious change in the workflow! In the light of this, I'd pass the theory (which was based on the assumption that everything else was kept constant - as I stated before) about alkaline sizing and/or alkaline (or - more likely - less acidic) gum. As Katharine says, humidity has a lot (LOT!) effect on printing speed, so, now I think *not pre-humidifying the paper anymore* is the actual/real reason of your speed decrease. (BTW, pre-humidification is my standard practice. I use a ultrasonic humidifier now, was using near boiling temperature hot water before...)
BTW, sometimes bits and pieces of pigment/dirt (small protrusions on the print's surface) and whatnot will cause small fisheyes that are almost impossible to fix. Moreso with some pigments; I have this phenomenon more often with PV19 Rose for instance. Try to keep your developing water clean and clean your prints from bits and pieces. (Such as not well dissolved pigment particles, hair...) Also try harder to size evenly; uneven and excessive sizing may cause fisheyes too.
Originally Posted by Jon Harwood
Lukas, I don't personally see any particular advantage to glutaraldehyde, and I don't think glutaraldehyde is better than glyoxal, which is my preferred hardening method. I didn't test the glutaraldehyde extensively because of the issues I had with the fumes, but the tests I did run showed no advantage for the glutaraldehyde. I don't seem to have on my site a comparison of printing gum on glyoxal vs glutaraldehyde, but I do have a comparison of glutaraldehyde vs printing on unsized paper, where I preferred the result on the unsized paper to the result on the glutaraldehyde-sized paper. If you're interested in that comparison, go to my page on sizing and scroll down to the first set of pictures you come to, and its accompanying text:
Originally Posted by Lukas Werth
You'd have to ask someone else the question about brushing it on separately.
Thank you, Katharine, this is exactly what I wanted to know. I will stick with my glyoxal then. By the way, just to let you know, when I harden by brushing on the Glyoxal later, I dilute it further, adding about 3cc of glyoxal to 50cc of water.