I have been getting a number of very good questions and comments from readers and I've been trying to decide the best way to go about answering them.  It has been my thought that I'd like to see people just dig in and try an emulsion.  Most things are clearer after a little hands-on.  But, the quality of the questions leads me here.  If the mission of The Light Farm is cooperative research with the end goal of a body of work, the greater the input, the better. 

If you have questions, of just about any shape or size relating to making emulsions, please contact me at 'editorat thelightfarm.com' (replace at with @).   These will be moderated, but I can't imagine a good question that I won't try my best to answer, and if I can't, it will be added to the "Good Research Questions" list for any emulsion maker to try to answer.  The best knowledge starts with the best questions.

The following questions came to me this morning (4/3/08) from a private message on the analog photography website, APUG.  My great thanks for great questions.

Q: All of the paper emulsions are unwashed, is that correct?

A: Yes, the paper emulsions currently posted on The Light Farm are unwashed.  Most slow speed, contact printing type emulsions are unwashed.  The paper substrate absorbs any salts that might crystallize out.  The faster, bromide emulsions, meant to be coated on glass or film (i.e. non-absorbent) or emulsions with ammonia are usually, if not always, washed to remove the excess salts and to bring the emulsion pH back down to neutral by removing the high pH ammonia.

Q: I noticed that you specified adding the chemicals in a specific order.  What is the logic behind this?

A:  Less logic than I wish I could pretend.  I am trying to go through the old literature and backward engineer many of the recipes.  They are typically for very large quantities and often use materials I can't get or don't want to use.  You couldn't get me to have hydrochloric acid or nitric acid lying around.  I go through a dozen similar recipes and try to get the gist of them and understand their similarities and differences, and then put together something that will work with the tools and materials I have on hand.  That is the extent of my chemical engineering expertise.  The recipes I have published here have worked for me dozens of times if I unfailingly follow the worked-out procedure.  The additions of the chemicals is one such procedure, along with time and temperature.  Each addition changes the nature of the soup to that point.  The addition of the acid changes the pH and therefore the potential solubility of the chemicals that follow.  When I get a recipe nailed down, I stop and consider it done and move on to a new exploration.  I often have not followed through on every possible variation of procedure.  There are almost certainly equally good ways to make a particular recipe, but if I haven't tried it, I won't publish it.  I'm looking forward to the input from other emulsion makers.  The more information, the better.  It may be that citric acid, for example, can be dumped in at any time, but at this point I can't Fair Witness that.

Q: During the finish, you have the melt at 40-51C, then you add a few things, filter and put in a water bath...what is the reason for the 65C water bath?

A: This refers to the contact paper recipe, right before coating.  Right after the finals have been added, the emulsion is too warm for coating.  Without a temperature jacket, it would be too cold and stiff for coating by the end of the session.  It is my philosophy to make it as easy (and cheap) as possible to hit that sweet spot where the emulsion is good to go for the whole coating session.  I've found, during my own personal work flow, that if I filter too-warm emulsion into a beaker nested in a larger beaker with enough cool water to jacket the smaller one, and then set the emulsion, in this jacket, on a 65C hot plate, the water jacket heats up at the same rate as the emulsion is cooling down -- resulting in as near a constant, perfect temperature as you could want - with minimal fuss or expense.

Q: (How long) Do you leave the emulsion in that bath? or...is this just to keep the emulsion warm while coating? 

It usually works out to just leave the emulsion in the waterbath jacket through the whole coating session.  But, it doesn't take any time at all to get the feel for the materials.  I can tell when the emulsion is too warm and thin to coat well and I'll pull the small beaker out of the water jacket and swirl it around a couple of times.  This is usually enough to cool it down to the right temperature.  If the emulsion feels like it's getting too cool and stiff, I'll put the beaker directly on the 65C hot plate for a minute.

Q:  How much emulsion do you end up with?

A:  The '♥'emulsions make just about 250 ml/recipe.  I almost always divide this up into two parts for two separate coating sessions.  A half recipe covers about 400-500 sq. inches of surface. 

Q: I notice that you are always spritzing the emulsion with Everclear...why do you do this?

Bubbles are the bane of emulsions.  The little buggers can really screw up an otherwise great coating.  Everclear is a surfactant.  It breaks the surface tension of the bubbles and poof! gone.  Spritzing delivers enough to do the job, without adding enough liquid to change the viscosity of the melt.  Just about any time I see froth, I pull out the Everclear.  An additional virtue of the stuff is that I swear you can get a buzz from just breathing the aerosol.  Everclear is near 100% hooch.  Nothing wrong with being a happy emulsion maker.

Addendum: 4/04/08:  I have been seriously outclassed in the humor department - and it's Chemistry Humor, to boot!  The poser of the above questions replied with this: 

"One important thing though...I should point out that if you mean 'hooch' as a word meaning FUN, I guess you could be right, but if you are thinking chemical shorthand, the enjoyable stuff would be OHC2H5.  HOOCH on the other hand , is FORMIC acid, and used in the way you describe, formic acid is more likely to irritate than please!"

And, one more question:

Q:  You start out making the emulsion at 40 deg. C? and make the final additions (just prior to the last filtering & coating) at 10 degrees higher?

A: This is about the dance of variables.  Gelatin changes characteristics with each melt and re-solidification.  The temperature at which each melting takes place also affects the next melt.  For our purposes, hard bloom gelatin melts best at 40C or slightly above.  On the other hand, increasing temperature is related to increased speed of emulsion.  There is a danger point, though, where too high a temp for too long pushes the emulsion into fog.  50+ degrees C for the length of time it takes to add the finals, seems to be the right temperature for both maintaining the gelatin in a completely melted state and warm enough to give the emulsion just a little more speed, without risking fog.  

It can't be overemphasized that making emulsions is as much an art as science.  That is why so compelling and fun.  Once you are comfortable with a few variables and have one recipe reliable for you, change with bold impunity and take notes.  There is nothing worse than discovering a EUREKA emulsion and not knowing how you got there.