In emulsion-making, like many other pursuits, once you get up the initial learning curve of following a recipe to produce a good photographic emulsion, a whole new world of exploration seems to open up in tinkering with the recipe. In my case, I’m interested in successfully making larger batches at a time.
I’ve had some hard-earned experience lately in what *not* to do, and can share some insight from that experience while creating a topic that I haven’t found any discussion about here on apug (or anywhere else for that matter).
When scaling a home-brew emulsion-making recipe to produce different volumes, the ratio of ingredients and temperature hold times should all remain the same. Scaling the amount of ingredients is straightforward, temperature hold times are fairly straightforward as well.
A tricky aspect especially for scaling up is maintaining the same cool-down times. For first ripening and chemical/second ripening, this means controlling the cool-down time after the hold at the specified ripening temperature(s). The actual cooldown times can be measured for the original volume, and then replicated for the scaled amount. For larger volumes, the emulsion can be divided into several containers of original volume and then combined as the emulsion is setting (mind the cooldown rate when it’s in the fridge) or active cooling can be used to control the rate of temperature change (i.e. putting tubing in the emulsion with cool water flowing through as the emulsion is constantly stirred)..
The other hiccup is how the precipitation stage is impacted by the larger volume of silver nitrate and salts that need to be combined. Kodak AJ-12, for example, calls for adding silver nitrate to the salt solution at a rate of 20ml/30seconds for 10 minutes followed by 10 minute ripening. Scaling up the volume 4x (for example) would mean precipitation iat 20ml / 30 seconds takes 40 minutes. This entirely changes the timing of the ripening and causes significant problems with the resulting emulsion due to the change in the distribution of the grain size as well as longer heating of the gelatin.
So obviously not only is the precipitation rate inportant, but also the total time required to combine the solutions. What I’m curious about is, when scaling the volume, can the precipitation rate be increased (shortening the total time of precipitation) to *approximately* result in similar grain size distribution as the emulsion made in the original volume, and what does the scaling relationship look like?
As I think about how to scale the recipe properly by adjusting the precipitation stage, my hypothesis are as follows:
I think to ensure the grain size is kept small enough to remain in suspension for the % gelatin in the recipe, the total precipitation time should remain at or near that of the original recipe. This will of course change the characteristic curve of the emulsion (my though is lower contrast and more delicate tonality in shadows and highlights)
I think you would also want to increase the amount of gelatin added after ripening. Or, perhaps start with a larger amount of gelatin in the salt solution to reduce grain growth and maintain a precipitation rate closer to the original.
Of course, to avoid these variables, the original volumes could be made in serial and then combined for washing. But then of course you’re not learning anything (even if you have to learn the hard way).
There’s other aspects to worry about: storage, preservation, etc., but my focus is on correctly scaling a recope to produce same or similar results. Or perhaps recipes cannot be scaled up, and doing so requires making one from scratch (or finding a different recipe specifically put together for the amount you want to make).
Thoughts from our learned emulsion makers?
-Jason
I’ve had some hard-earned experience lately in what *not* to do, and can share some insight from that experience while creating a topic that I haven’t found any discussion about here on apug (or anywhere else for that matter).
When scaling a home-brew emulsion-making recipe to produce different volumes, the ratio of ingredients and temperature hold times should all remain the same. Scaling the amount of ingredients is straightforward, temperature hold times are fairly straightforward as well.
A tricky aspect especially for scaling up is maintaining the same cool-down times. For first ripening and chemical/second ripening, this means controlling the cool-down time after the hold at the specified ripening temperature(s). The actual cooldown times can be measured for the original volume, and then replicated for the scaled amount. For larger volumes, the emulsion can be divided into several containers of original volume and then combined as the emulsion is setting (mind the cooldown rate when it’s in the fridge) or active cooling can be used to control the rate of temperature change (i.e. putting tubing in the emulsion with cool water flowing through as the emulsion is constantly stirred)..
The other hiccup is how the precipitation stage is impacted by the larger volume of silver nitrate and salts that need to be combined. Kodak AJ-12, for example, calls for adding silver nitrate to the salt solution at a rate of 20ml/30seconds for 10 minutes followed by 10 minute ripening. Scaling up the volume 4x (for example) would mean precipitation iat 20ml / 30 seconds takes 40 minutes. This entirely changes the timing of the ripening and causes significant problems with the resulting emulsion due to the change in the distribution of the grain size as well as longer heating of the gelatin.
So obviously not only is the precipitation rate inportant, but also the total time required to combine the solutions. What I’m curious about is, when scaling the volume, can the precipitation rate be increased (shortening the total time of precipitation) to *approximately* result in similar grain size distribution as the emulsion made in the original volume, and what does the scaling relationship look like?
As I think about how to scale the recipe properly by adjusting the precipitation stage, my hypothesis are as follows:
I think to ensure the grain size is kept small enough to remain in suspension for the % gelatin in the recipe, the total precipitation time should remain at or near that of the original recipe. This will of course change the characteristic curve of the emulsion (my though is lower contrast and more delicate tonality in shadows and highlights)
I think you would also want to increase the amount of gelatin added after ripening. Or, perhaps start with a larger amount of gelatin in the salt solution to reduce grain growth and maintain a precipitation rate closer to the original.
Of course, to avoid these variables, the original volumes could be made in serial and then combined for washing. But then of course you’re not learning anything (even if you have to learn the hard way).
There’s other aspects to worry about: storage, preservation, etc., but my focus is on correctly scaling a recope to produce same or similar results. Or perhaps recipes cannot be scaled up, and doing so requires making one from scratch (or finding a different recipe specifically put together for the amount you want to make).
Thoughts from our learned emulsion makers?
-Jason
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). Start at 2x. Double the amount of each addition proportionately. Cool down time can be hastened by a cool or cold waterbath. The characteristic curve should pretty much stay the same that way.
