How to make a faster unwashed emulsion?
I made an interesting emulsion following instructions for an unwashed bromide emulsion found on "Silver gelatin" book.
20 g gelatin
16 g potassium bromide
125 ml water
mix sol. at 50°C
20 g silver nitrate
raise temp. at 40°C
mix B into A at slow rate
the emulsion is supposed to be ready right after digestion is complete; no washing or additives are strictly required
This emulsion works fine for me. Requires two coatings for a contrasty image. ISO rating has been a little problematic. Under the enlarger it needs at least 120" F4 to print its deepest black. Average exposure required is 160-240" at F4. In one word: SLOW.
I was attempting to use the same emulsion for glass negatives. The emulsion sticks very well to glass without subbing. A little sanding of the edge of the glass helped.
The problem is its really poor sensitivity to light... Which is probably ISO 3. But since it is especially sensitive to Blue and UV, the ISO drops when shooting in artificial lighting. Is there a way to make it faster? Say ISO >10? Should I modify a little the above formula? Another solution I've considered is to dip the plate into developer right before exposure, pretending it is a wet plate. Kalotypes work in a similar way... but then the obvious advantages of a dry plate are gone.
Any suggestions or recipes for other unwashed emulsions? I'd prefer to stick on unwashed emulsions. Handling a more complicated emulsion-making process would be too much for me now.
Unfortuately, those formulas assume active gelatin to do the chemical sensitization step and therefore your speed and contrast are too low to be practical.
For that emulsion, try heating with 50 - 100 mg of sodium hypo pentahydrate / mole of silver added as a 1% or 0.1% solution in distilled water. The addition should be at 60 degrees C and the emulsion should be held for about 1 hour.
Unfortunately, I cannot predict the exact amount or time for you as this must be done by trial and error or you get fog. So, I advise you to try it on a small portion of the emulsion first. I methods for doing this elsewhere.
Proper finish should increase speed by 2 - 3 stops, and contrast by 1 or 2 grades. My emulsion for enlarging paper is typically the same as for Ilford MGIV paper wiht the grade 2 filtration. But, I use an entirely different prep.
BTW, the excess bromide will retard the action of the hypo sensitization, another reason that I can't give you a prediction for what will happen.
maybe I will try... But I forgot to mention that I used tap water instead of distilled water. For some weird reason, the batch with distilled water didn't work well. The one I'm using is the second one, made with tap water. It works fine, no spots, no fogging, etc. Since I use tap water, there could be some salts in the emulsion already. My tap water is indeed alkaline.
"Silver gelatin" suggests mixing B (silver nitrate) into A (pot. bromide) at a rough 5ml over a period of 10 minutes. Do you think that raising considerably the mixing time of the two emulsion components will determine an increase in speed at the cost of a lower contrast? Would there be any risks of chemical fogging?
Ah, and while I'm here I have another question for you master of photographic gelatin: how long the shelf life of such emulsion would be? Since this batch worked very well I was considering to prepare a larger amount (say 500 ml or up to one liter). Of course I'd store it in a dark bottle in the fridge. Since the emulsion contains active gelatin and is unwashed, I can't compare it with commercial emulsions... I have had some of these for over than one year without problems... Also, how about re-melting? While many people say that is advisable to break the gelatin in smaller pieces to avoid re-melting, I actually never did that - again with commercial emulsions. But never had a problem.
Last edited by Fulvio; 12-02-2006 at 03:32 PM. Click to view previous post history.
Fast addition generally gives slower speed and higher contrast, whereas slower addition tends to increase speed and lower contrast. Just a very rough generalization.
If you use chlorine in your water, it will add a small amount of chloride to the emulsion, but that is probably insignificant. If you have ozonolosis, I have no idea what it will do.
Acid tends to increase contrast slightly with some emulsions and alkalinity tends to decrease contrast and speed up hardening. It decreases the lifetime of the melted emulsion with hardener in it.
Pepper grains, or black specks in your prints is from large grains which aggregate. It is usually due to not having enough or good gelatin. I never got it at Kodak, but I see it here with different gelatins or different batches of the same gelatin.
Your only recourse might be to dilute the silver more or add more gelatin. But, that might create other problems. The emulsion would become too dilute or too viscous.
Bad news. Yesterday I coated a large number of sheets of paper with my emulsion. The emulsion was made about ten days ago. It looked great in the beginning, now looks like shit. I got a lot of fogging and stains on the prints. I believe that the emulsion has to be used right away after preparation or within the next couple of days. I think I'll give up the idea to make my own emulsion, I already spent the equivalent in silver nitrate of half kilo of factory grade emulsion...
Perhaps it is the tap water... I don't know why but I had occasionally pepper grains with distilled water. Using inert gelatin delivers pepper grains as well, a very flat contrast and very ugly tones. With food gelatin the tones are great, no fogging at all, nice contrast and the emulsion spread easily, without evident bubbles. It sticks nice on glass, without subbing or glass manipulation. But then... appears to have the shelf life of a fresh yogurt...
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Sorry to hear of your problem. My emulsions are usually used up rather quickly, but I have kept them for about 6 months with no problem. I do go in and out of problems. These mainly come from errors, or changes in batch of a given chemical, but with tweaking the problem is solved and I have more information to pass on.
Your formula is not all that different than mine, and I have no pepper grain with that formula. I add the silver over 10 mins, and then ripen for about 30 minutes. I then follow it with the hypo treatment I described for 1 hour at 60 deg. Then I add final addenda such as spreading agent and hardener.
I get good black tones and good whites. The speed allows an 8x10 print to be made in about 12" at f11. The prints compare well with commercial product. But, to get there I too had to use up a bit of silver nitrate as my first results were rather bad. I had to tweak things to fine tune my technique to match the equipment I have. I don't have a fancy Kodak emulsion lab any more.
But, none of my unwashed emulsions stick to glass well at all during processing. They appear to beforehand, but float off during processing. The washed emulsions stick to the glass. I expected this, but I wanted to try it anyhow.
I might add that bromide is a powerful restrainer for bromide emulsions, and so the result you have is not unexpected for an unwashed emulsion.
If you want to try again, double the gelatin and the water in part A. Raise the temperature of both A and B to 55 degrees. That should fix up the pepper grain. Then, try the hypo treatment. That should fix speed and contrast.
hmmm yeah perhaps I'll give another try in a very small amount... Actually if I'd prepare only the amount I need each time and use it immediately there wouldn't be so many problems. The fact is that not having the possibility of preparing large batches of emulsion, then it becomes a really time consuming task. Also, in my (limited) experience emulsion coated papers can't be stored for a very long time, even if the emulsion is factory made. That means: few emulsion, few papers...
Pepper grain isn't the only problem. Fogging was evident in the last batch, after less than a dozen days passed. And the emulsion was stored in a fridge, remelted only twice.
I'm looking forward to test an Efke/Adox emulsion. Costs about 15 euros per 250 ml, but my local supplier hasn't got it yet (and has been a month of waiting). The same shop sells silver nitrate for ca. 16 euros / 25 grams. In another shop I can buy 100 grams of silver nitrate for about 40-50 euros... Add a small cost of bromide and gelatin, there isn't really an huge economical advantage unlike other processes or chemistries.
Apart from the fun of making your own emulsion and having it ready whenever you need it, a real advantage would be if you print bromoils. Not every paper works with this tecnique and only a few commercial emulsions are good for that. Any emulsion that contains hardeners is unsuitable for bromoil. The only commercial emulsion I've tried that takes bromoil bleach is the Foma. The bad news is: they don't sell it outside Czech Republic (and it's only 30 euros per kg)...
About glass coating: I always had problems in sticking emulsions like Foma or SE1 from Silverprint on glass, even with a small subbing of the plate; I have another subbing recipe - will try that asap. I was very surprised when the home made emulsion didn't lift when processed (I had on a few plates just some frilling at the borders)...
I make emulsions in batches as small as 120 ml which contain 5 grams of silver nitrate. At the rate of 12 ml / 8x10, this allows me to make and use the emulsion at one time and get 10 sheets of paper for printing.
I don't usually remelt as that is not a good idea. I use a spatula or spoon and rubber gloves to remove what I need when I need it. Remelting adds fog to the emulsion. Each remelting is like restarting the digestion.
In fact, with one emulsion and addenda combination that I coated as a double batch, I could see the results change from coating #1 to coating #18. It was slight and gradual, but since I run a step wedge with all prints I could see the change. The emulsion was slowly changing at the coating temperature.
I am scheduled to give a workshop in Montana in June, if that is any help to you.
then I believe that remelting killed my emulsion
Originally Posted by Photo Engineer
my initial assumption that an unwashed homemade emulsion could be remelted was probably a mistake
I wonder then why factory made emulsions can be remelted a large amount of times without visible deterioration... For example Foma sells bottles of 1 kg of emulsion and that goes a long way... Before it's finished I have melted and remelted the same emulsion a few dozen times (also considering that two coatings are required with Foma)...
My emulsion too required two coatings to deliver a good print. With a single coating the dmax was too low.
nice, too bad I live thousands miles away
I am scheduled to give a workshop in Montana in June, if that is any help to you.
you should also make a live video conference, while you're there...
there's a lot of nice old printing workshops in the US and there's very few in Europe... If I win the lottery I would spend years traveling from a workshop to another and learn everything...
The emulsions sold commercially also warn you about reheating. It is in the labels and mentioned in the book "Silver Gelatin". In addition, they may add some stabilzers which are expensive and hard to get.
For example, Thymol (10% in iso-propyl alcohol) at about 1 drop per 100g of emulsion will prevent mold and fungus. I've mentioned addition of Tetra Aza Indene as a preservative. This is also discussed on Jim Brownings web site in his emulsion making portion of the paper.