Refrigeration and remelt, why ? why not ?

[di de]

Hello everybody here,

I'm new to emulsion making and I'm enjoying it !
First of all, thank you everybody for the invaluable amount of informations displayed on this forum.

So far, I've made about ten small batches of emulsion (Denise's AmBr + Hypo finish) for paper negatives (mostly 4x5" and 5x7") and I get pretty consistent results shooting at about 8 ISO.

Now, I'm working on emulsion for printing on paper. Chloride emulsion is ok, pure Bromide emulsion is ok, but I tried Chlorobromide emulsion from the light farm book (two times) and all I got was a uniform grey fog...

I think that one hour rippening time is too much in my case...

But I was also wondering why this emulsion didn't need to set and to be refrigerated for at least 8 hours as the bromide one...
And by the way, why an emulsion for paper doesn't need to be washed ?

Well, I guess there will be many more questions coming... thank you in advance...
(I hope my english is understandable, I'm writing from south of France)

 

[dwross]

Hi di de. Always nice to see a new emulsion maker. Sorry you're having trouble with ClBr emulsion. Shouldn't be the case. May I ask a few questions? Are you following the recipe exactly, or are you making modifications? What is a "hypo finish"? What are your safelight conditions? The emulsion is very fast, but if you didn't get light fog with the bromide paper, then that's probably not the case. What developer are you using? The only touchy thing about the paper is the developer options. An aggressive (very active) developer will fog the paper. It's not happy with most commercial MQ or PQ formulations. D76H and D23 are both excellent, and simple and inexpensive to make. Other than that, it's one of the most foolproof and flexible recipes I make. For my own personal work, it's the one I usually use.

There are a few reasons to refrigerate emulsions. The most important is for washed emulsions. You have to "set" the emulsion so that you can shred it for washing. That's only required for emulsions coated on non-absorbent surfaces -- glass or film. Paper absorbs the by-product salts that might crystallize out on a hard surface. A second reason is just for convenience. You can break up the making process into convenient chunks of time. Last, additional ripening time can be planned into an overall recipe to increase contrast and density.

Good luck, and please feel very free to ask any and all questions, here or to me personally. My email is editor@thelightfarm.com, but I'm trying to get back in the habit of reading APUG every morning. The feedback is very important to growing the medium of handmade emulsions. Think of how many mistakes were made and questions asked as cyanotype, or carbon, or platinum printing were being perfected! Best, d

 

[di de]

Hello Denise, thank you for your answer.

Hypo= hyposulfite of soda = sodium thiosulfate
Hypo finish = sulfur sensitization (I gain a full stop with your AmBr emulsion)

As for my ClBr emulsion, the only thing I've changed is that I divided all ingredients by two (but I kept the same temperature and same ripening time)
I don't think my safelight is in cause and I used Ilford Bromophen developer which gave me good results with other formulas (and also lith developer because my goal is to make lith prints with my own paper).

So if I read you well, there is no mandatory need to refrigerate any emulsion that is not washed ? In the TLF book, you write to refrigerate the bromide enlarging paper emulsion and not the ClBr, even if the two are not washed. Is it only to increase contrast and density ?

 

[dwross]

I think you'll have better results with D76H, or D23 with added borax at 1/2 to 1/3 the amount of the metol. I've only used Ilford PQ, but I wasn't happy at all with the results. The ClBr emulsion is a different beast (make-wise) from most other emulsions. It's the reason you can get excellent results from both contact printing and enlarging, with a range of negative characteristics, in an emulsion that is very simple and inexpensive to make. It only asks to be allowed to be picky about developers .

I've never done lith printing. I'm eager to see what you can do with the process and handmade emulsions.

Yes, the set, remelt, extra ripening time greatly improves the profile of the bromide emulsion.

 

[Photo Engineer]

Many Cl/Br emulsions are very hard to make and vary a lot depending on mixing. This is due to the closeness of the solubilities of AgBr and AgCl. I have stayed away from them for the home emulsion maker as I have no suitable and transportable formulas. By transportable, I mean able to move from site to site and give the same results. I'm sure Denise will recall her difficulties with one of my emulsions at the Montana workshop and then her problems moving it to the west coast. We recently tried to make the Bromide emulsion from the book at GEH for a workshop, a move of about 20 miles from my home, but changes in Silver Nitrate and Gelatin. We had to re-write the entire formula.

So, don't be discouraged. It will work, but the AgCl/Br may require some adjustment in ripening time or mixing.

Heating and chilling repeatedly is a no-no. The emulsion can fog. One heat cycle to finish or ripen or both and then chill. Remove only what you need for one session and melt, then use.

PE

 

[di de]

Thank you Denise and PE

I might be wrong but I don't think that the developer is the problem here. As PE said, I think I have to adjust the process to my setup.
But I've already made a successful ClBr emulsion and basically the only differences were ripening time, refrigeration and adding Potassium Iodide final. Even though it lacked a bit of speed for enlarging, it worked beautifully for contact lith print (see image below).

Denise, here is a contact lith print made from home made paper negative onto home made paper with home made developer... even my 5x7" camera is home made !...
My goal is not to seek perfection of a clean, crisp and sharp realistic image, I'm rather looking for "atmosphere"...

 

[Photo Engineer]

A dash of KI will often fix up fog in emulsions, but if you add too much it can cause more fog.

PE

 

[di de]

I added 2ml of a 1% solution for 100ml of emulsion and in this case it seems to make all the difference...

 

[dwross]

di de,
Wonderful print!

 

[di de]

Thank you Denise
I'm pretty happy with it, I think I'm gonna start a series on this subject with home made emulsions for shooting and printing.

 

[dwross]

It's going to be a beautiful series. Can hardly wait to see it.

 

[di de]

Some prints are drying right now...

 

[di de]

I made another test with another emulsion, this emulsion worked perfectly well with setting and refrigeration for about 15h then remelt and coating, but when I coated straight after ripening and chilling down to about 35°C but without setting and refrigeration, then I got poor dull results, no deep blacks, unusable...

 

[Photo Engineer]

Sounds as if some sort of keeping is continuing then when you cool it. There are other possible explanations.

PE

 

[dwross]

di de, Great research!
Different recipes are well...different. That's what I find infinitely challenging and fun.

The emulsion is indeed continuing the "ripening" process as it cools all the way down to refrigerated temperature. In addition, the emulsion is continuing that ripening at different rates throughout the refrigerated container. The emulsion along the outside of the container gets cold fastest until it stops changing, but the emulsion in the center stays warmer, longer, so continues ripening for a longer time. The process when you remelt the emulsion is similar. All of this adds to the vigor and contrast and density range of the emulsion. Not all recipes require this, but for the ones that do, it makes all the difference. d

 

[di de]

Well, if it needs two stages to work, then I'l make two stages and voilà !...

 

[Photo Engineer]

Oh, and another thought. As an emulsion sets up as you chill it, the heavy grains do indeed sink or settle to the bottom of the container thus causing a gradation in speed and contrast from the top to bottom. Therefore, it is a good idea to stir while cooling a new emulsion and then when cool, put it in the fridge.

PE

 

[di de]

Thank you for this thought but... can't it be useful to have such gradation in speed and contrast ?

 

[Photo Engineer]

Yes and no unfortunately. You can exploit it, as you suggest, but it can confuse you if you are testing an emulsion or trying to repeat results.

From your original post it might be useful to ripen (or digest) the emulsion a little longer before you continue using it in any way. Chloride ion is also a solvent and can cause extended slow digestion.

PE