Blythtypes: New 'positive-working Cyanotype system'

[Hologram]

http://modernholography.org/blythtypes/

http://modernholography.org/wp-content/uploads/2018/12/Blythtype_Nov_2018_2.pdf

 

[Andrew O'Neill]

If that example is the best that the process can offer... I'd rather scan in the Kodachrome, and print its digital negative in traditional cyanotype.

 

[koraks]

I think this is a fascinating development. Sure, there seems to be room for optimization, but the achievement of (1) remarkably high sensitivity and (2) extension of sensitivity into the red spectrum are nothing short of remarkable.

One particular avenue that would be interesting to pursue is that of in-camera direct positives.

 

[nmp]

Does it look like it is sensitive to visible light, since the authors are advocating projecting the image onto the paper. No big deal if it is positive acting, but definitely if one can use digital/analog projector as the source of image, which would be indeed a novelty.

The process itself looks like has a few more steps than the easy and simple old cyanotype which I think is its main charm.

Anyway, thanks for sharing. Always interested in learning about new inventions in image-making.

:Niranjan.

 

[NedL]

The pdf says that thionine ferricyanide is formed on the paper and then made light sensitive with EDTA. What is the light sensitive compound?

Is it somehow related to blueline or diazo? I guess not since prussian blue is formed.

 

[nmp]

The pdf says that thionine ferricyanide is formed on the paper and then made light sensitive with EDTA. What is the light sensitive compound?

Is it somehow related to blueline or diazo? I guess not since prussian blue is formed.

It is different from diazo technology, but it seems the general principle of positive-acting chemistry is similar.

In the former, diazonium salt disassociates when exposed. The unexposed molecule then can complex with the coupling agent to give the blue azo dye. In this case, unexposed thionin ferricyanide is insoluble. I could be wrong, but this is the actual molecule that is photosensitive. Most likely (again a conjecture on my part without thoroughly researching, photochemists please weigh in) the EDTA/DEA forms the "sensitizing" dye - to make the formulation sensitive to visible zone of light. On exposure, the thionin ferricyanide decouples to revert to the soluble potassium ferricyanide which is then washed out. Now you are left with the insoluble thionin ferricyanide which then can react with the "developer" ferrous sulfate to make the all-familiar prussian blue.

This is how I understand so far.

:Niranjan.

 

[nmp]

It is different from diazo technology, but it seems the general principle of positive-acting chemistry is similar.

In the former, diazonium salt disassociates when exposed. The unexposed molecule then can complex with the coupling agent to give the blue azo dye. In this case, unexposed thionin ferricyanide is insoluble. I could be wrong, but this is the actual molecule that is photosensitive. Most likely (again a conjecture on my part without thoroughly researching, photochemists please weigh in) the EDTA/DEA forms the "sensitizing" dye - to make the formulation sensitive to visible zone of light. On exposure, the thionin ferricyanide decouples to revert to the soluble potassium ferricyanide which is then washed out. Now you are left with the insoluble thionin ferricyanide which then can react with the "developer" ferrous sulfate to make the all-familiar prussian blue.

This is how I understand so far.

:Niranjan.

Well at the bottom of the word document the mechanism is spelled out in quite detail, superseding my simplistic (if not erroneous) early take:

>>>>>>
In the imaging process light causes the dyed photosheet to bleach and momentarily to
produce a colourless compound known as leuco-thionin. This reduced form of the dye
then seeks to return to its non-reduced coloured form by reducing its ionically attached
ferricyanide anion to form thionin ferrocyanide. The proportion of ferricyanide ion
converted to ferrocyanide ion is dependent on the light intensity on that area and also of
course, the exposure time. In the highlight areas of the image, the conversion to
ferrocyanide can approach 100% and in the darkest areas the conversion can be almost
zero. When the exposed sheet is immersed in the acidic ferrous sulphate solution, the
famous Prussian Blue (PB) pigment forms only where thionin ferricyanide still exists. It
does not form when it meets thionine ferrocyanide. Therefore, in the highlight areas
very little Prussian Blue is formed. That therefore makes this a “positive-working”
system. However the ferrous sulphate solution. will also inevitably contain some
oxidised iron in the form of ferric sulphate, from molecular oxygen absorption.
Consequently, when ferric sulphate in solution meets any thionine ferrocyanide,
especially in the highlight areas of the image, it will also form PB. This can lessen the
whiteness of the highlights. But by keeping the solution fresh, the proportion of ferric to
ferrous sulphate will be low and its effect will be very slight. We think that most of the
thionin gets freed to be washed away as its soluble sulphate salt by a combination of PB
getting formed from the ferricyanide ions, and the very insoluble white ferrous
ferrocyanide being formed from the ferrocyanide ions.
<<<<<<

 

[Photo Engineer]

I suggest that one problem might be the use of a digital print paper as the substrate. The chemistry in them has caused me many problems with otherwise normal silver gelatin coatings due to the mordants and etc.. in them.

PE

 

[nmp]

I suggest that one problem might be the use of a digital print paper as the substrate. The chemistry in them has caused me many problems with otherwise normal silver gelatin coatings due to the mordants and etc.. in them.

PE

Interesting why/how they settled on the type of papers to use. As I understand, they seem to suggest the process only works on the papers they recommend. Would have been nice if they elaborated on the rationale for that. That which would help others who might try to experiment with different type of papers, particularly the traditional alternative process water color papers.