Quick question about % -- Spirit Sensitizing for Carbon

I'm hopping on the spirit sensitization bandwagon but have one question that I can't seem to find a straight answer to.

Currently I have a big bottle of 5% potassium-dichromate stock solution and 90% isopropyl alcohol made with pure water. If I mix these 1:1 and then brush onto my tissues, what's the final % I'm left with? How about 1:2 (stock PD : spirit)?

If I soaked my tissue in 5% PD, I would say that it's been tray sensitized at 5%; nice and simple. But since the purpose of the spirit is to quickly evaporate, I'm having trouble conceptualizing how much PD is left in the tissue. 10%?, 2.5%?, 5%?... aaggghhh

I just look at the total amount of dichromate I am delivering to the tissue.

For a 9x11" tissue (for 8x10 neg) I use 5ml of an 8% solution, diluted 1:3 with acetone (5ml:15ml). The final dilution does not matter -- I am introducing a set amount of dichromate to the tissue -- I can dilute it with 10, 15 or 20 ml of acetone -- it does not matter. 100% of the solution goes onto/into the tissue. In reality, I do try to be consistant (using the 15ml of acetone per 5 ml 8% Ammonium dichromate) so that the dichromate soaks into the tissue in the same manner every time -- one less variable to deal with.

So looked at another way, I am putting 5ml of an 8% Ammonium dichromate solution on the tissue -- that is 0.4 grams of Ammonium dicromate per tissue (with is about 100 sq inches) or 0.004 grams per square inch.

So if I am using 0.4 grams, carried by 20ml of water/acetone -- that is a 2% solution if one wants to look at it that way.

Ok, you had me at 8% and then you lost me with 2%.

Though, this does make sense, particularly, "I am introducing a set amount of dichromate to the tissue".

Is it fair to say that comparing %'s between tray & spirit sensitizing is not so simple?

I'm thinking along these lines;
- If you are tray sensitizing, the tissue is soaking up X amount of Y%-dichromate until saturation. Therefore, the amount of dichromate in there is determined by water temperature, soaking time, gelatin concentration, etc. But with spirit sensitizing, there's no guarantee of saturation, and it seems that 1 pass of the brush and n passes of the brush will give you widely varying amounts of dichromate in the tissue. Or is "saturation" reached fairly quickly in brush-sensitizing as well?

See, I'm all mixed up on this. At least I know enough to get started... I just wanna get it.

In short, let's say I have a negative that printed well with a tissue tray sensitized in 3.5% PD-solution. How can I achieve the same contrast/speed with spirit sensitizing?

Ok, you had me at 8% and then you lost me with 2%.

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very funny , you will need to cry more because there is a saying here , there is no milk to uncrying baby

holmburgers said:

Ok, you had me at 8% and then you lost me with 2%.

Though, this does make sense, particularly, "I am introducing a set amount of dichromate to the tissue".

Is it fair to say that comparing %'s between tray & spirit sensitizing is not so simple?

Click to expand...

Vaughn's right...when you're spirit (brush) sensitizing, you have to think in terms of the total dichromate delivered to the tissue, or more to the point, the total dichromate per square inch. An 8x10 tissue needs 4x as much dichromate (4x the surface area), if all other factors are equal.

holmburgers said:

I'm thinking along these lines;
- If you are tray sensitizing, the tissue is soaking up X amount of Y%-dichromate until saturation. Therefore, the amount of dichromate in there is determined by water temperature, soaking time, gelatin concentration, etc. But with spirit sensitizing, there's no guarantee of saturation, and it seems that 1 pass of the brush and n passes of the brush will give you widely varying amounts of dichromate in the tissue. Or is "saturation" reached fairly quickly in brush-sensitizing as well?

See, I'm all mixed up on this. At least I know enough to get started... I just wanna get it.

Click to expand...

With tray sensitizing, you have no (easy) way of knowing how much dichromate you're introducing to the tissue. There is no guarantee that the tissue will become saturated in a tray-sensitizing situation. All the factors you mention play into that.

When spirit (brush) sensitizing, most people flood the tissue with ~1/2 of the total required volume, using the brush to spread the puddle evenly across the surface of the tissue, brushing until all of the acetone has evaporated, and the brush starts to drag slightly on the surface of the gleatin, which has gotten slightly tacky from the small amount of water introduced. Then apply the other 1/2 the volume, and repeat brushing. You're not "painting on" the dichromate, as your metal picture of above would seem to indicate. (i.e. transfering the solution from a container to the tissue by means of the brush.)

I also dip my brush into a dish of acetone before sensitizing. Anecdotally, it seems there is less dichromate washed out of the brush when I do this (presumably because a brush wet with acetone will absorb less of the sensitizing solution, but this is just a guess.)

holmburgers said:

In short, let's say I have a negative that printed well with a tissue tray sensitized in 3.5% PD-solution. How can I achieve the same contrast/speed with spirit sensitizing?

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There's no way to know for sure. But you should be able to get pretty close with 2 or 3 tests, I would imagine. The best part is, then you'll know how to treat any negative of yours that printed will with 3.5% PD in a tray.

Best of luck--

Greg

Just delete Vaughn's last sentence ... he was simply playing devil's advocate with it.

holmburgers said:

...In short, let's say I have a negative that printed well with a tissue tray sensitized in 3.5% PD-solution. How can I achieve the same contrast/speed with spirit sensitizing?

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Like it was already mentioned, a couple of tests, or printing sessions and you should have it nailed down. Too many variables to know otherwise. Tray sensitizing can be done in a consistent way, but it is difficult to translate it into spirit sensitizing.

One would need to know how much dichromate had gotten absorbed into the tissue in the tray to be able to compare the two methods. If one uses tray sensitizing to the point where the gelatin will not absorb anymore, one could work out the volume absorbed by measuring the remaining sensitizer. Then one might be able to compare it fairly well with other methods. I suppose one could do a test just using water -- I'll let someone else do that! I guess temperature and tissue thickness would come into play, too.

And as mentioned, one tends to push a puddle of sensitizer around with the brush, rather than "paint it on". I find it important to continue brushing until there is no more liquid sitting on the surface of the tissue.

Have fun!

Just delete Vaughn's last sentence ... he was simply playing devil's advocate with it.

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Dang...busted! Five ml of my stock 8% Ammonium dichromate (AD) solution contains 0.4 grams of dichromate in the 5ml of water. For use, that 5ml is then diluted with 15ml acetone to yield a solution that contains 0.4gr AD suspended in a total of 20ml (5 ml water+15ml acetone) of liquid. So if one insists on knowing the actual dilution used on my tissue, it is 0.4gm/20ml = 2%. Of course knowing just the percentage is not enough info for spirit sensitizing...the total amount must also be known.

Ok guys, this has been great. Thank you very much!