Ammonium Dichromate replacement for Carbon printing

[sanking]

"When you tested the emulsion with the step wedge…. this is a step edge transparency that you contact printed onto the emulsion sample. Then you developed that and took a picture of the wedge print with a digital camera. What are the steps in the wedge… 1 stop per step? "

In this case I scanned the step wedge since it is small enough to do so, and being on smooth Yupo texture is not a problem as it can be with some papers. Each of the step wedges is log 0.15 density, or the equivalent of 1/2 stop. A full stop in sensitometry is log 0.3.

"Can you develop in warm water, or do you have to use other chemicals?"

Development is in warm water, same as with tissue sensitized in dichromate.

"Why would you want to brush on the sensitizer rather than mix it in the emulsion. To avoid marginal emulsion stability when sensitized? Or set contrast grade at print time?"

In monochrome printing I like to set the contrast grade at the time of printing, to be able to fine-tune it for a specific negative. This is the equivalent of being able to work with a variable contrast paper in silver printing, where you can fine tune contrast with filters. With pre-sensitized tissue you are stuck with the contrast that is built in.

With color my thought process on this would be different as you would want to start with tissue with known and consistent characteristics.

Sandy

[gth]

"When you tested the emulsion with the step wedge…. this is a step edge transparency that you contact printed onto the emulsion sample. Then you developed that and took a picture of the wedge print with a digital camera. What are the steps in the wedge… 1 stop per step? "

In this case I scanned the step wedge since it is small enough to do so, and being on smooth Yupo texture is not a problem as it can be with some papers. Each of the step wedges is log 0.15 density, or the equivalent of 1/2 stop. A full stop in sensitometry is log 0.3.

"Can you develop in warm water, or do you have to use other chemicals?"

Development is in warm water, same as with tissue sensitized in dichromate.

"Why would you want to brush on the sensitizer rather than mix it in the emulsion. To avoid marginal emulsion stability when sensitized? Or set contrast grade at print time?"

In monochrome printing I like to set the contrast grade at the time of printing, to be able to fine-tune it for a specific negative. This is the equivalent of being able to work with a variable contrast paper in silver printing, where you can fine tune contrast with filters. With pre-sensitized tissue you are stuck with the contrast that is built in.

With color my though process on this would be different as you would want to start with tissue with known and consistent characteristics.

Sandy

Ok, I understand.
Would it be possible to make pre-sensitized tissue in certain fixed contrast grades and then tune it with an additional brush coat at print time.?
That would depend on if you can get ANY sensitizer into the emulsion with brush application.

[sanking]

Ok, I understand.
Would it be possible to make pre-sensitized tissue in certain fixed contrast grades and then tune it with an additional brush coat at print time.?
That would depend on if you can get ANY sensitizer into the emulsion with brush application.

The answer is I don't really know how well this would work. You can brush the sensitizer on the tissue but as I may have mentioned, it does not seem to penetrate very deep into the layer of gelatin. There may be a solution to this by addition of some penetrating agent, but for now I am clueless.

The mechanism of how dichromate penetrates the gelatin layer is not widely understood for that matter. Some people have claimed that you must tray sensitize to get the dichromate to the bottom of the tissue layer, but that is clearly not the case.

Sandy

[gth]

Sandy, do you know if the Speedball Diazo Sensitizer has been determined NOT to work with gelatine?

In the big thread on this matter at APUG seems they started with the Speedball because it is readily available. But the conclusion is not completely clear that the Speedball stuff will not work. I think it was determined NOT to work, but it was also a matter if too much sensitizer was used in the first experiment.


/gth

[sanking]

Sandy, do you know if the Speedball Diazo Sensitizer has been determined NOT to work with gelatine?

In the big thread on this matter at APUG seems they started with the Speedball because it is readily available. But the conclusion is not completely clear that the Speedball stuff will not work. I think it was determined NOT to work, but it was also a matter if too much sensitizer was used in the first experiment.


/gth

I gathered that Speedball is capable of producing an image, but how well it does that in comparison to dichromate is not apparent from the thread.

It seems that once Charles Berger noted that the sensitizer used in the Ultrastable was 4,4 ' - diazidostilbene -2,2' - disulfonic Acid Disodium Salt Tetrahydrate (now known as DAS) the conversation shifted to it.


Sandy