Emulsja jodo-bromowa-Radosław Brzozowski-iodo-bromide emulsion13

To make an emulsion

At first glance, making an emulsion sounds reasonably easy, especially if you understand some English and search the internet. Without much difficulty you will find pdf versions of old books devoted to emulsion making and literally dozens of recipes. You will read those, usually rather brief descriptions, lists of ingredients and it will seem to you that all those people who told you how hard the process is were simply having you on.

Then you go to the darkroom, take all the chemicals you have collected in the meantime and start working. And a few hours later you start asking yourself the question: what went wrong? After all in the workshop or in the book everything seemed so easy. All I can say is this; if you don’t give up at the early stages, this is a question you will keep asking yourself more often than you have ever expected.

There are a few reasons why things go wrong and why making emulsions is not an easy task and it makes sense to know them before you start trying. Especially if your aim is a film emulsion.

  1. Available information

There is a lot of information. OK, you need to look for it and it really helps if you understand English, but the information can be found. Personally I managed to collect something like a hundred books on the subject. Some of them are the old books in PDF format, some expert publications from the 60s and 70s – much more valuable but also more costly and difficult to find. The most important ones are the limited editions used internally within photographic companies or at universities and never intended for outsiders. These are by far the most precious and nearly impossible to get. Though, I did get them.

The problem is, that all those books aren’t very helpful. Pre-war literature is full of omissions and errors, frequently deliberate ones (after all the authors didn’t really want to give away all the information. Then, why should they really. Just to give one example; in a monumental book containing something like a hundred different recipes , a description of a lab as well as the equipment and production technology as used on industrial scale, one detail was forgotten. Namely the author never mentioned the fact that ammonia added to the emulsion had to be neutralized next. This information was not present anywhere in the book and without it, all the recipes were useless to a beginner who is not able to spot the omission.
The second issue is the knowledge required to understand the more modern texts. If we don’t have at least a minimal understanding of emulsion chemistry and some experience in making them, understanding the texts will be hard. Especially in the case of Polish publications loaded with technical jargon.

The next issue is the recipes themselves. They are all similar and use the same materials, seemingly simple. Only that the secret of a successful emulsion is not in a the materials or even proportions but in the way in which they are combined. Without a very detailed description of the process of making the emulsion, the recipe itself is not much use.

2. Materials

Seemingly, these are only too simple. See the sample list below:

silver nitrate, potassium bromide, ammonia, gelatin, sulphuric acid, potassium iodide.

Nothing special, you would say. Everything can easily be bought. Ooooops, you could hardly be more wrong. After a few tests (probably failures), we will learn that a p.p.a. potassium bromide is not pure enough and needs to be purified before we use it for making emulsions. We will also learn that silver nitrate coming from one manufacturer might be pure enough, and from another; not quite. Even though both are described as p.p.a. We will learn many unpleasant truth about most chemicals available on the market.
Above all, however, we will learn that gelatin doesn’t always mean the same thing. It hardly ever means the same thing.

First you will learn that it is bovine gelatin that is used in emulsion making, not the readily available pork gelatin. And bovine gelatin is hard to get in the EU. Secondly, it will turn out that all pre war recipes, the recipes that are the simplest and most readily accessible assume using the so called active gelatin that have been out of production for decades. Without them, the recipes aren’t much use. Of course, in theory every edible gelatin might be an active gelatin but then, it might not. Or it might be too active for example. Even if we, somehow, manage to get gold of a true, active photographic gelatin (as I did), you will learn that each of them has different properties, different levels of activity. As a result a recipe that works perfectly well with one gelatin will be an abysmal failure with another. As a result each new batch of gelatin means tests in order to adjust the recipe or the lab procedure. Theoretically a gelatin you bought by chance may prove to be perfect; this is the way things were in the past (long, long ago), but it is neither likely nor predictable. What is more, if it turns out that the gelatin we got works, it will be impossible to buy more of the same material.

If we take more modern recipes, we will find out that they use the so called empty or inert gelatin, prepared especially for emulsion work. Something like a decade ago a whole system of controlling their quality and describing parameters was in existence, unfortunately now IAG is more focused on jelly making. Theoretically, photographic gelatins are still available,but we never know if they will work for us. What is more, a particular gelatin may work perfectly well for one emulsion and fail abysmally in another. I tested three gelatins that are currently available on the market and I managed to get a working emulsion with each of them, but only one of the gelatins worked in all three emulsions. So only one of them appears to truly be an inert photographic gelatin.

Once we have collected all the basic materials, it will soon transpire that additional materials are needed such as antifoggants or sensibilizing dyes. In a pinch we can substitute the latter with erithrosine (used for jellies), stabilizers however can’t possibly be substituted. Yes, emulsions can be made without them, but they will not last long and their parameters such as ISO can’t really be optimized. We will also have to forget about things such as chemical sensitization (in most cases this means we will have to forget about speed and contrast). You had also get friendly with fogging then; something that can be lived with in case of negatives, but not positive prints. Stabilizers are still in production and theoretically can be bought. Only in practice this borders on the impossible.

Let’s assume that you now have all the ingredients or that you decided to make one of the simpler emulsions, a single run emulsion with no stabilizers or sensibilisation. The problem here is that, with the possible exception of the absolutely most primitive (and not very useful) recipes, every little factor has huge impact on the product. A minimal change in temperature during the precipitation or ripening will produce an emulsion that is significantly different (possibly useless). The same holds true for the time; is the nitrate added over a period of 60 or 90 seconds? Did we start by adding it copiously and ended with a tiny amount, or the other way round? Each of these will be of monumental importance and may either improve or destroy the emulsion. Let me stress this; each tiny variation will lead to obtaining a different emulsion which means that if we choose to later sensitize it, it will respond very differently to all the additives. It can be seen at first glance that getting repeatable results is hard, at least if we don’t have an electronic pump to control the speed with which ingredients are added. And we are still talking about simple, single run emulsions.

I would have forgotten; water matters too. And it should be distilled water made from deionized one (distillation alone doesn’t guarantee an appropriate level of purity). It would be even better to use multiple distillation. I am not saying that emulsions can’t possibly be made with deionized water; sometimes they can and I have made such emulsions. But water like this does not guarantee repeatability and may lead to problems as in yielding the emulsion useless. We need to remember that the amount of some chemical used in producing the emulsion is smaller than the amount of impurities in a glass of tap water.Let’s assume, you have overcome all the obstacles so far and managed to get all the materials and make a working emulsion. Most likely it will not be very fast. In my case emulsions made with active gelatins usually turn out to be about 3ISO (though I did not try to push them excessively). Now the emulsion needs to be washed (water temperature about zero deg. Centigrade, you need more than 20 litres for a small batch), protected against bacterial growth (this part is actually easy) and… coated on glass. Easy? After all this is what you have been doing with collodion. Yeah, right. Though it is easier than the actual making of the emulsion.

Of course, we may also attempt to make more sophisticated emulsion, make the grain more homogenous (for instance by separating the precipitation and growth of crystals). But this adds an extra level of difficulty. We can also go for chemical sensibilization but this is an altogether different story. And something that, at least theoretically, shouldn’t be done with active gelatins. Theoretically, because it was chemical sensitization that enabled me to convert a 1,5 ISO emulsion to a 20 ISO emulsion.