Red-Sensitive Potassium DCG

[chromoprinter]

Hi everyone,
I'm currently reading Graham Saxby's Practical Holography and interested in trying out Jeff Blyth's recipe
for making a Red-sensitive Dichromated Gelatin Emuslion on glass.

The recipe calls for

75 cm3 1,1,3,3 Tetramethlyguanidine (TMG)
20 cm3 Glacial Acetic acid
5g Potassium Chromate (K2CrO4)
.4g Methylene blue
75g Gelatin

I want to work with coating my own emulsion on glass. I was originally thinking of using potassium dichromate (K2Cr2O7) used in gum dichromate printing (which is easier to find),
as a substitute for potassium chromate. I'm not sure if the substitution would work or would mix incorrectly with the TMG.
I figure it would be safer to work with the requirements of the recipe then mixing chemistry.

Has anyone worked with this recipe or would recommend a better recipe for red-sensitive dichromated gelatin?
And is there a vendor that distributes the chemistry for this method or a similar method?

My goal is to coat my own holographic plates and to avoid buying an expensive laser to expose them.

Please let me know.

Thanks.

[Joe Farina]

Potassium chromate is available on eBay. I noticed one seller in Japan who does ship worldwide (if you're in the US, there are cheaper sources on eBay who ship only within the US).

Everything except the TMG is available on eBay. Unfortunately, finding the TMG is a real problem. So I would be sure that you have a source for it, before buying the other chemicals.

Jeff Blyth's system works very well, a number of forum members have used it, including me.

[jeffblyth]

Hi everyone,
I'm currently reading Graham Saxby's Practical Holography and interested in trying out Jeff Blyth's recipe
for making a Red-sensitive Dichromated Gelatin Emuslion on glass.

The recipe calls for

75 cm3 1,1,3,3 Tetramethlyguanidine (TMG)
20 cm3 Glacial Acetic acid
5g Potassium Chromate (K2CrO4)
.4g Methylene blue
75g Gelatin

I want to work with coating my own emulsion on glass. I was originally thinking of using potassium dichromate (K2Cr2O7) used in gum dichromate printing (which is easier to find),
as a substitute for potassium chromate. I'm not sure if the substitution would work or would mix incorrectly with the TMG.
I figure it would be safer to work with the requirements of the recipe then mixing chemistry.

Has anyone worked with this recipe or would recommend a better recipe for red-sensitive dichromated gelatin?
And is there a vendor that distributes the chemistry for this method or a similar method?

My goal is to coat my own holographic plates and to avoid buying an expensive laser to expose them.

Please let me know.

Thanks.

Hi, I have just spotted your post a bit late but I hope I can just clarify something about potassium dichromate versus chromate. You can readily convert dichromates into chromates by adding the right amount of alkali to a stirred solution of say 5% potassium dichromate until it gets to a pH of about 8 to 9.
The chemistry really is straightforward enough. I will just run through it for future reference , and maybe add it to Colin's Holowiki.
Potassium chromate is the potassium salt of Chromic Acid : H2CrO4 where the 2 acid H's
are substituted for 2 K's
Now to see how potassium Dichromate (K2Cr2O7) is made up,
please just note down the total formula from adding one potassium chromate (K2CrO4) to one chromic acid (H2CrO4).
You then get a total of K2H2Cr2O8 . now just take away 1 H2O and you get K2Cr2O7.
So dichromates are all just 1:1 combinations of chromate salts with chromic acid. There is of course no need to use potassium hydroxide to do the conversion, Na OH
will work just fine.
I have just calculated that 100 ml of 5% K2Cr2O7 will require 1.36 g solid sodium hydroxide to convert it all to the chromate form.
(The colour of the solution changes from the intense orange yellow to a light canary yellow when the conversion is complete.)
Some of you will have already spotted that 5% K2Cr2O7 solution has got more chromium compound in it than the intended 5% K2 Cr O4 solution.
To make it equivalent you need to cut down the volume of solution used by a third. But I don’t think this is a critical issue .
Jeff

[holorefugee]

Thank you Jeff!

http://holowiki.org/index.php?title=DCG ... o_Chromate