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Hans2008
05-21-2009, 09:51 AM
I have been trying to make phthalated gelatin according the following procedure:

1] 8g gelatin in 80ml water at 40C.
2] Adjust PH to 10 with 10% NaOH.
3] Slowly add mix of 0.8g Phthalic Anhydride in 6.4ml Acetone, while at the same time keeping PH at around 10.0
4] After all the mix of step [3] has been added, wait 10 minutes (while monitoring that PH stays at 10.0).

Now to test that I did it correctly I then proceeded to lower the PH to below 3.5 with H2SO4. This should have caused the gelatin to precipitate out of the solution, but it did not. Does anyone know what I have done wrong here?

Photo Engineer
05-21-2009, 12:00 PM
What is the temperature? It should be decreased along with the decreasing pH.

OTOH, why make it when it is so plentiful ready made in the market. Kodak will sell it, Rousselot will sell it, Kind and Knox will sell it and the Photographers Formulary sells it. The latter sells in small quantity, but the former 3 only sell in larger quantity.

PE

Hans2008
05-21-2009, 01:33 PM
What is the temperature? It should be decreased along with the decreasing pH.
I did the acylation at 40C. Then I dropped the temperature to 35C and tried the precipitation by lowering the PH.


OTOH, why make it when it is so plentiful ready made in the market. Kodak will sell it, Rousselot will sell it, Kind and Knox will sell it and the Photographers Formulary sells it. The latter sells in small quantity, but the former 3 only sell in larger quantity.
I need for my purpose a gelatin of very high bloom number (around 300). Because I just want to test the effect of phthalated gelatin in a holographic emulsion I cannot afford to order a very large quantity. And I cannot find this type of gelatin at photoformulary.com

Photo Engineer
05-21-2009, 04:47 PM
Well, commonly about 250 bloom is the highest you can normally get without special order, and one company told me that they would not guarantee anything above 250 BI. As for phthalation, this generally can reduce BI or viscosity.

The formation of the coagulum is usually done between 25 and 35 deg C. I have never run the acylation but I have been told that it is not an easy reaction.

I might add that coagulation forms with greater difficulty in the absence of silver halide, and that acylation does not always go to the level you expect due to crosslinking and other factors.

PE

Hans2008
05-21-2009, 04:57 PM
Well, commonly about 250 bloom is the highest you can normally get without special order, and one company told me that they would not guarantee anything above 250 BI.
So true. I was lucky to find a gelatin maker in Germany (Gelita) who makes a very high quality high bloom gelatin. They sent me two samples of de-salted gelatin. One with bloom 280 and one with bloom 300. They are by far the best gelatins I have ever used and gives me the smallest grains I ever had. In solution they are nearly completely transparent and the fact that they come desalted saves me a lot of work. If possible I would prefer to modify this gelatin over using a phthalated gelatin of lower quality.

Photo Engineer
05-21-2009, 09:12 PM
Gelita is a division of Kind and Knox gelatin. When I spoke with them, they said that they would not supply anything over 250 and if I special ordered a drum they might have some 275 that they could send. In general, they told me that the higher the BI, the lower the quality.

I stooped to lowering the make temperature to get finer grain. I would guess that my emulsions differ quite a bit from yours.

PE

Ray Rogers
05-21-2009, 10:36 PM
Gelita is a division of Kind and Knox gelatin.
PE

Or versa-vise ;)

sanking
05-21-2009, 10:46 PM
I have no idea if it will serve your purpose but one could buy a 300 Bloom gelatin from the United States Biochemical Corporation.

http://www.usbweb.com/category.asp?cat=118&id=16047

Unfortunately you might have to have someone in a lab or at a university buy this for you as last time I checked they did not sell directly to individuals.

Sandy King

Ray Rogers
05-22-2009, 02:43 AM
I have an unused 310 bloom gelatin...

Hans2008
05-22-2009, 03:03 AM
I have now tried the experiment with another bovine gelatin as well (250 bloom bovine gelatin). But again without result. I must be doing something wrong here...


I stooped to lowering the make temperature to get finer grain. I would guess that my emulsions differ quite a bit from yours.
Yes, in my emulsions it is of vital importance that the grains are very small. In the order of 10nm. If a holographic emulsion is not nearly transparent to the eye before coating it is not likely to work well.

Photo Engineer
05-22-2009, 09:35 AM
I have no idea if it will serve your purpose but one could buy a 300 Bloom gelatin from the United States Biochemical Corporation.

http://www.usbweb.com/category.asp?cat=118&id=16047

Unfortunately you might have to have someone in a lab or at a university buy this for you as last time I checked they did not sell directly to individuals.

Sandy King

Sandy;

This is pig gelatin which has a vastly different isoelectric point. IDK of ever hearing of it being made into a PA gelatin.

Hans;

From what I know, your results or lack thereof is not unusual in making PA gelatin.

PE

Emulsion
05-24-2009, 03:38 PM
Could you please explain how to de-salt gelatin? What impact does this have on the results?

Thanks from,
Emulsion.

Hans2008
05-26-2009, 09:42 AM
Could you please explain how to de-salt gelatin? What impact does this have on the results?

An easy way to de-salt gelatin is to cut a gelled gelatin into small cubes or shred it to noodles. Then wash those gelatin bits in several baths of de-ionized water. This procedure removes most of the salts that have remained in the gelatin during it's manufacture. If those salts are not washed out before precipitation of the AgBr grains upredictable or unwanted results can occur. For example: If a lot of chloride ions are present in an unwashed gelatin, this can cause unwanted grain growth during the precipitation stage.

Hans2008
05-29-2009, 11:33 AM
Ok, my last test worked. This time I introduced the phthalic anhydride below the surface of the gelatin instead of dropping it in.
Also, I made a fresh solution of the anhydride in Acetone (I don't know if that solution spoils, but I did not want to take any chances).
And, I did the reaction at a slightly higher PH of 10.5.

This time the gelatin precipitated as very fine particles when I lowered the PH to below 4. I think that for washing the gelatin the procedure might not be very suitable. At least not with ultra-fine grains because it takes quite a while for this precipitate to settle to the bottom of the glass jar. All this time the emulsion needs to be warmer than 32C and this increases the grain size. But then, I did not really do the experiment for washing the gelatin, but rather to see if I get a better emulsion with the phthalated gelatin.

Photo Engineer
05-29-2009, 02:11 PM
Remember that the gelatin will coagulate faster in the presence of silver halide. In fact, if you use all phthalated gelatin at the start of the precipitation, you will get a putty like coagulum. It will also generally give you finer grains. This might be of some benefit. I have posted a picture of this here on APUG.

You may want to consider UF wash though.

PE