It did take a while, but the end is in sight. It is almost the end of work on another emulsion. OK, it is not new because probably no one makes perfectly new emulsions from scratch. Maybe except for a handful of people working for Ilford or Kodak. Nevertheless, the task of adapting a pre war emulsion to modern materials isn’t exactly and easy one.
An emulsion is a seemingly easy thing. If we look at a list of ingredients, it appears to be as simple as it gets and it appears, that few things should be easier than to combine them into an emulsion. The reality turns out to be different. First of all we make an emulsion blindly, so to say. We don’t have any means of learning what is happening in the pot at any particular moment. Nor can we assess progress or correct the process in its course. Of course, we could do it if we had high end equipment, but few if any amateurs happen to have an electronic microscope handy. If we did, there would be much more we could do to learn what is going on; we could assess the growth of crystals, their shape and so on.
As most of us don’t have that sort of equipment, all we can do is guess what is actually happening in the pot, what reactions are taking place and what their results will be. We create the conditions that should give the results we desire, and hope that things will go well. This, however, can only be assessed once the process has been finished (or at least is very advanced). We can’t see a problem as it happens but only guess/work out what went wrong once we see that the results are not satisfactory.
Unfortunately, we can only make any form of assessment when the process is well advanced or even complete. This not only means that in each case we have to complete the time consuming process before we see if everything went as expected but, first of all, in many cases we can only guess at what went wrong. And things will naturally go wrong more than once, especially in the process of creating a new recipe. Actually, the problems that happen and imperfect emulsions made on the way are the only available source of information about what takes place during the synthesis that we have and analysing them is the only way we can learn what happens at each stage of the process. This in turn means that we have to repeat the whole process time and time again, introducing tiny changes one at a time until eventually the problem is solved and a working emulsion is obtained.
Let’s take a typical example; an emulsion that shows excessive fogging. We have devoted something like 12 hours to making it, we feel that we have done everything right and yet, the emulsion still shows fogging. What went wrong? Is contamination to blame? Split milligrams are enough to destroy the whole batch. Was something wrong with the safelight. Even light filtered through a red filter will eventually accumulate and fog the emulsion. Maybe the filter has lost its properties with time? Or maybe there is something wrong with the gelatin? If it came from different batches there can be tiny differences. Or maybe something was wrong with the water? Of course any chemical used in the process might have been imperfect, even if all were p.p.a. The maybes can be multiplied almost without end and each and every one has to be tested and this means another emulsion that needs to be made.
And maybe, again maybe, the reason lies somewhere else. After all we are not copying someone’s modern emulsion but adapting a formula coming from the past, a formula created for different materials, for active gelatins, for a different scale of production (yes, this is important too). What is more, the original emulsion was made under conditions that are unknown to us which is a hurdle in itself. Every single element is of key importance and requires adjusting the recipe or the procedure.
Simply copying someone else’s emulsion and the procedure for making it is difficult enough and will involve numerous errors and require a number of tests. Adapting an old recipe is an entirely different story and a different level of difficulty. If you only consider the fact that an additional stage, the chemical sensibilisation has to be added because modern gelatins are not active any more. The amount of the sensitizer would be easy to establish if we knew the size and shape of the silver halide particles created in the emulsion. But we don’t, we can only make assumptions based on the procedure used. And these assumptions need to be tested and tested and tested once more. And each test means making a new batch of emulsion. And this, in turn, means another day of work. Hopefully another day bringing us closer to our objective, but only too often it ends with an emulsion that still doesn’t work. Of course, every failure should bring us closer to success, assuming we made sure the whole process took place in exactly the same way as before. Every change, every alternation of a couple of degrees Celsius or even a few seconds may lead to creating an emulsion that is different than assumed and to the information collected being useless. It is a paradox of sorts that seeing the same error a few times is a good sign in itself.
In any event, it appears that the process of adapting an old emulsion by Eder and of working out a procedure for making it is approaching completion. As of today, problems only appear at the final stage and concern values that can be measured more or less easily. Nevertheless, the precise amount of reagent and time is unclear, even if they have been narrowed down. One milligram; too little. Five milligrams; too much. Will three yield good results? As the problems appearing in each case are almost identical, we can at least assume that the rest of the process has been stabilized and unless something bad happens, success is a few tests away. Unless, of course, this is one of the emulsions that can’t be sensitized properly and will not produce satisfactory results.
Of course then, the emulsion will need to be sensitized spectrally to be orthochromatic but, at least in theory, this should be slightly easier.