Substituting Potassium Dichromate for Ammonium Dichromate?

[Tom Taylor]

Can Potassium Dichromate sucesssfully be substitied for Ammonium Dichromate in Dick Sullivan's Mix for Cyanotype Stock Solution B found on page 154 of the James book?

Thanks,

Thomas

[Mike Wilde]

Sorry, my cyanotype reference books and articles are not right in fornt of me; they are at home.

I beleive if you account for the atomic weight differences of the potassium versus the ammonium you will be fine; it is really the dichromate ion that we are looking for when it comes to contrast adjustments with this process.

I cannot recall if there is a longevity of the stock solution issue that favours the use of one over the other.

[Tom Taylor]

Thanks Mike.

Before I posted my question I did a search and found a response to a similar question, but not on the Cyanotype formula, by Sandy King where he stated it was ok to substitute recommending substituting 117 parts of Potassium for 100 parts of Ammonium. I just got off the phone with B&S (it's Dick Sullivan's formula) and they said it was OK to substitute.

Thomas

[Tom Taylor]

I beleive if you account for the atomic weight differences of the potassium versus the ammonium you will be fine; it is really the dichromate ion that we are looking for when it comes to contrast adjustments with this process.

I cannot recall if there is a longevity of the stock solution issue that favours the use of one over the other.

Good idea!

Since the potassium, K₂ is more than twice the weight of the ammonium (NH₄)₂, I increased the amount of possasium from .8gm to 1.25gm to keep on the safe (i.e., lite) side. It should work out

Thomas

[Tom Taylor]

As a follow-up it would have been more correct if I had used the ratio of mole weight of Potassium Dichromate to Ammonium Dichromate rather than the ratio of Potassium to Ammonium present in each. That would have brought the ammount of Potasium Dichromate to add to 1gm and not the 1.25gm that I actually added. It's been a long time since I worked chemistry problems But I'm still within the ballpark.)

Thomas

[Vaughn]

Fun with chemistry!

[wildbillbugman]

Watch out! I have had severe skin reactions to sodium dichromate, but never to potassium or ammonium dichromate ! I had not had such reactions to anything since 1974, when I reacted to isopropyl methacrylate, but not to Isopropyl acrylate.
Wierd,
Bill

[Tom Taylor]

I'm hooked!

Coastal Defense



Toyo 810G.

Thomas

[gmikol]

I'd say maybe a little light, and the contrast seems a bit off to my eye, but it's really good for a first (?) try. Where is it? Doesn't look like any I've seen on the OR/WA coast.

--Greg

[Mike Wilde]

One of the challenges of mixing traditional and cyanotype prints is that cyanotype usually needs a longer scale negative. I get good punchy cyanotype prints from negs in the Dr of 1.5 to 1.8.

With cyanotype experiments and new papers or sensitizers or sizings I always print a 1/2" x4" 1/2 stop series step wedge. It actually is taped to the side of contact frame glass, so that it is there ready to go. Slide the neg to expose first time next to it, and slide it into the UV box.