# The key to the door of crystal types

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• 08-29-2007, 12:35 PM
Photo Engineer
Simply, the developer changes the form that the silver metal takes and therefore influences the structure of the image. This can be done for any shape or size of crystal.

It is more complex than this due to solvent developers, edge effects and etc. but that is it in a short form.

PE
• 08-29-2007, 08:07 PM
PhotoSmith
Thanks PE. It was good to learn a little about silver grain structure in emulsions from you. I appreciate it!
• 08-29-2007, 08:33 PM
DBP
Fascinating as usual, Ron. But I must admit that my first thought on seeing the title of the thread was that some new age types stumbling onto this through googling 'key', 'door' and 'crystal' were going to be in for a surprise.
• 08-29-2007, 09:04 PM
Photo Engineer
Well, there is a double pyramid shape, but I doubt if it will focus any special energy for healing. :D

PE
• 10-05-2012, 12:38 PM
kb3lms
Temperature Effects?
Reviewing this thread again with equations in hand, I had a new question. PE, I guess this is directed your way or maybe Kirk would know as well.

The crystal type chart in the OP gives pAg at 70C. But since the Ksp of bromide changes with temperature, pAg and vAg change with temperature too. If you are trying to make say, cubic grains, at a different temperature like 50C, do you aim for the same pAg, say 7, for a cubic grain? (Or t-grain, or octahedral or whatever you want to make)

-- Jason
• 10-05-2012, 12:58 PM
Photo Engineer
To give na example, at 60C with 0.1 m/l NaBr, the vAg = -39.54 mv but at 50C it is 43.60 mv. At 50C it requires a sollution of 0.08 m/l to get to -38.16 mv or back to the original.

At 50C the pAg = 9.99 at 0.08 m/l
At 50 C the pAg = 10.08 at 0.1 m/l
At 60 C the pAg = 9.98 at .1 m/l

You can see vAg tracking pAg here but with a 5 mv difference in vAg but only about 0.1 units in pAg. Since I have not done the exact experiment you describe, I think you will find it best to try yourself. I predict little difference. The size may differ more than the crystal habit under your suggested changed conditions.

PE
• 10-05-2012, 02:51 PM
kb3lms
So as long as the ion concentration doesn't move too far out of the range of your intended target, there will more likely be size differences but not great differnces in the habit due to temperature? Then it sounds like when you are designing, you would pick your target pAg such that you had some leeway for temperature and ion concentration drifts. You would want to be in the middle of the range, not at the ends, which would make sense.

Using equations from your book and RIT in a spreadsheet along with the chart you gave I have been reading through some papers from RIT and looking at what the authors did and plugging their numbers back into the model to see if they made sense along. Mostly, they do but some are iffy in that they are close to the edge of the range. Kind of a thought/paperwork exercise. It was raining the last couple of days and this was something interesting to play with.

I've got a silver electrode built but haven't gotten the reference made yet. But I have so many experiments planned it's insane - some of them may yet even get done! :D
• 10-05-2012, 05:27 PM
Photo Engineer
Well, the RIT work is not as rigorous as that done at EK. After all, we had to control vAg all over the world.

PE
• 10-05-2012, 06:12 PM
Prof_Pixel
Quote:

Originally Posted by Photo Engineer
Well, the RIT work is not as rigorous as that done at EK. After all, we had to control vAg all over the world.

PE

Aren't the values defined by the Nernst equation?
• 10-05-2012, 06:49 PM
Photo Engineer
Yes, they are as well as that of the Debye Huckle equation. However, the experiments at RIT may not have been as exacting as those at Kodak. The EQG (Emulsion Quality Group) and CELS (Committee for Emulsion Lab Standards) made sure that a mv was a mv the world round.

PE
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