Potassium Dichromate solution for carbon printing

[Pasto]

Does potassium dichromate in solution (6%) go bad on the shelf? Just wondering if I can make a bigger quantity and store it or rather just what I need to sensitize 8-10 sheets of paper at a time....

 

[Gerald C Koch]

It should keep for a long time. How much were you thinking of making?

 

[Vaughn]

Keep organics out of it and it will last indefinitely. I keep bottles of various dilutions ready for printing...some are years old.

 

[Pasto]

I'm thinking of making a couple of litres and then draw from it what I need as I go along....maybe just a 6% solution to dilute as needed, but if the shelf life is so long then it would make sense to make smaller quantities at different dilutions.

Thanks for your input.

 

[Gerald C Koch]

I'm thinking of making a couple of litres and then draw from it what I need as I go along....maybe just a 6% solution to dilute as needed, but if the shelf life is so long then it would make sense to make smaller quantities at different dilutions.

Thanks for your input.

While a dichromate solution will keep well it does pose a safety issue. I would only mix enough to last a reasonable amount of time for your work process say 3 to 6 months. Any spillage should immediately be cleaned up and not allowed to dry as the dust is hazardous.

 

[Pasto]

Good point Gerald. I'll take your advice.

Thanks again.

 

[Vaughn]

I'm thinking of making a couple of litres and then draw from it what I need as I go along....maybe just a 6% solution to dilute as needed, but if the shelf life is so long then it would make sense to make smaller quantities at different dilutions...

I use 5ml of my 'normal' 8% stock solution of AD per 8x10 tissue (actual size 100 sq inches). So two liters would be enough for 400 8x10 prints! I work slow enough that that would last a long time. Just do not put it in the fridge where someone might think it is orange juice! (Does not need to be in there, anyway.)

If one uses a bath of AD or PD to sensitize the tissue in, that contaminates the dichromate with organics (gelatin) and it will not keep to the next printing session.

 

[Pasto]

I've been trying with 8ml but it would still make a lot of prints! Maybe best stick with about 500ml quantity...

 

[Vaughn]

If you make one dilution, you can figure out how to dilute it to make weaker solutions. But for consistency, keep the total volume of liquid constant. That is (for example), if you use 8ml of a 10% solution but wish to increase contrast by using half the dichromate, then instead of just using 4ml of the 10% solution, use 4ml of it added to 4ml water (also keep the amount of the spirit carrier, alcohol or acetone, the same).

But I find having different solutions already mixed up (I have 2%, 4%, 6% and 8%), that there is less chance for a math error and less handling of the dichromate solutions...especially in workshop situations! I use 100ml bottles for most of them and a 250ml bottle for my usual 8% solution.

 

[Andrew O'Neill]

I spirit sensitize always mix up 100ml (AD) stock solution. That'll give me 20 prints. Like Vaughn, I keep various strengths on hand. I keep them in small brown energy drink bottles I bring over from Japan. They keep indefinitely mixed with water but not spirits. It's like graded paper in a bottle!