To 90 grams of distilled water, add 5 grams of photo grade gelatin and bring it to 40 deg C. Stir constantly. When dissolved and there are no floaters of gelatin, add 3.51 grams of reagent grade Sodium Chloride (NaCl). (I find dissolving the gelatin first is best)
Note, stirring should be continuous, and strong, but should not whip air into the gelatin salt mixture. Don't overdo the stirring, but don't underdo it either. Overdoing it will give you bubbles, and underdoing it will lead to a bad emulsion with foggy large grains.
In another container, dissolve 5.1 grams of Silver Nitrate (AgNO3) in 10 ml of distilled water.
Bring the gelatin and salt solution to 60 deg C with stirring. Turn out the room lights and turn on a red or yellow safelight, and then add the 10 ml of silver nitrate to the salt solution as you continue stirring.
Set a timer for 5 minutes and hold the mixture at 60 deg C for 5 minutes then place in a light tight container and place in the refrigerator. This will keep for about 1 month with no deterioration, perhaps longer.
You can coat this on about any surface with a paint brush if you remelt it at 40 deg C. I suggest a good camels hair brush with loose bristles removed.
If you have trouble with even coating, add a drop or two of photoflo 200 to the melted emulsion. If you need hardening, add a few drops of 10% chrome alum to the melted emulsion. If you add any hardener, the emulsion must be used as soon as possible or it will set up to a putty like mass.
Exposure time will typically be in the contact paper range. I've used about 3 seconds to normal room light. You should get a good black image with a contrast of about 2.
Ron, I don't know which formula you are referring to but speed of ISO 25 is not hard to beat without spectral sensitization. There are many key points but iodide distribution should be tightly controlled so that dislocation can be introduced at the very end of grain growth stage. Plus, precipitation condition should be controlled to reduce coefficient of variation (especially to the larger diameter side--smaller grains will simply be junk grains that simply and harmlessly waste silver) so that the digestion condition for S+Au can be optimized. Also, incorporation of dopants that act as shallow electron traps is important.
Regarding the coating problem. The ease of coating depends on the viscosity of the emulsion, which is determined by factors like gelatin concentration, gelatin avg molecular weight, coating temp, hardener, etc. I have found that a hardener that works slowly (taking a few days) is best for hand coating because they don't increase viscosity during the coating stage. Spread can be improved with a suitable surfactant, but most of the good ones are very bubbly and foaming becomes the problem with hand coating with brush. Many defoamers impaired spreading and adhesion in my experience. So I did some systematic search for suitable surfactant that maximizes the coating efficiency and produce very low foaming. Surprisingly, emulsion patents don't even mention the agents I use... though the agents themselves are not uncommon.
Originally Posted by Photo Engineer
It is possible to make your own liquid emulsions in the darkroom in about 45 minutes total time with only 7 chemicals. The results will be between slow enlarger and contact speed and will have contrast grades of about 2 or lower. This includes hardening agents and spreading agents.
Formulas for the emulsion are posted on the net or available from participants in this or other forums.
With additional work and at least one more chemical, you can achieve up to ISO 25 and ortho sensitivity. These formulas are not posted or currently available, but I understand that they may be in the not so distant future.
Your biggest problems with the commercial and home grown emulsions alike will be adhesion to the substrate, spreading (coating uniformly) and hardening. Commercial emulsions often remain unsold on the shelf for a long time. They are not high volume items. Therefore, they may deteriorate with time. IDK, I have avoided using them.