peeling rc paper for paper negative

[Loris Medici]

I don't think paper expansion is the cause here, because the base material of RC papers is very stable dimensionally...

Just a quick thought about the blurring - maybe during the 3 hour exposure the paper expanded due to heat? I expect the contact frame would have to be super-tight to prevent such thermal expansion over such a long time.

Regards,
Neil.

 

[z-man]

TOO MANY VARIABLES

1. the exp time of 2-3 hours is much to long as is the stated time for the tanning unit--the "cyanotype" material may be the problem-sounds like the senitised solution is deep in the support and/or not formulated properly-i allways start all my experiments with commercial "blueprint paper" material as it is so consistant and will get me into the ballpark fast

2. a single wt fiber base paper can easily be made transparent with "torch fuel"-this is liquid parafin that usually has citronella in it and has been descented --you could use regular kerosine but the fumes will be harsh--baby oil is ok but much too oily

3. resin ctd 'paper' is not paper-the reason for using it as a neg is that there is no fiber grain that will intrude into the print--HOW-EVER- the brighteners that are put into it flouresce very strongly under uv, and it may be that with such long exposures the very bright glow of the support(this would be visable under uv only ) is causing the 'bluring'

4. with so many variables it is very difficult to know what the actual problem is untill some kind of known constant is in the equation--blueprint paper and the tanning unit would be a easy way to test as both are constants

vaya con dios

 

[Neil Miller]

Loris - the RC negative is on top of the coated paper....

Regards,
Neil.

 

[Neil Miller]

3. resin ctd 'paper' is not paper-the reason for using it as a neg is that there is no fiber grain that will intrude into the print--HOW-EVER- the brighteners that are put into it flouresce very strongly under uv, and it may be that with such long exposures the very bright glow of the support(this would be visable under uv only ) is causing the 'bluring'

Are you sure, z-man?

Kentmere describe VC Select as "...The paper is 190 g/m² coated on both sides with 40 g/m² of polyethylene..."

Forte describes its RC range as "...Fortespeed is graded, resin coated (RC), black and white enlarging paper with a neutral
black image tone. Fortespeed papers are manufactured on a medium weight (175 g/m2)
paper base..."

Ilford, Kodak and Agfa spec sheets that I've read all say much the same - that RC is paper that is Resin Coated on both sides, plus other layers, like emulsion, etc.

Sounds like a lot of paper in 190 g/sm to me!

Regards,
Neil.

 

[Loris Medici]

Hi Neil,

I see what you mean - I took it the other way. Thanks for the clarification.

BTW, on my first assertion, I assumed Akki14 dried the coated paper thoroughly, to the point of being "bone dry". This is the usual procedure for many Cyanotype practitioners, because the speed and contrast of the emulsion is very sensitive to humidity changes. This, combined with the fact that it's hard to judge correct exposure from the printout (especially when it comes to delicate highlight tones) one will conclude that it's best to standardize / lock the parameters that way. (Using "bone dry" paper that is.)

Bone dry paper will not expand with heat, what causes the paper to expand is absorption of humidity from air, and heat from sun won't allow the paper to absorb enough humidity from the air to end up being expanded. Instead, humid paper will shrink when exposing under sun. (Bone dry paper won't change dimensions in those conditions.)

Regards,
Loris.

Loris - the RC negative is on top of the coated paper....

Regards,
Neil.

 

[Neil Miller]

Hi Loris,

Perhaps there are a lot of other tiny factors involved in this particular issue (blurring):

maybe the paper is not bone dry,
maybe the glass is thermally expanding and taking the neg with it,
maybe the wooden back is expanding and taking the paper with it,
maybe the different coefficients of the various materials used in the frame are warping it over the extended printing period and allowing less than perfect pressure?
Maybe there was just a smudge on the glass?

Who knows for sure? It's interesting trying to reason it out, though!

Regards,
neil.

 

[Philippe-Georges]

Ray;

He is talking about unpeeled papers which requires that the wax penetrate 2 layers of poly ethylene. This might not work. I have been told it would not.

If stripped, then it might penetrate to some extent.

I would agree that baby oil might be better than wax. It works on FB, but don't forget that PE is quite resistant to penetration even by baby oil.

PE

Dear PE,

Perhaps a very thumb question, but can the back plastic layer or RC paper be 'removed' wit an solvent like acetone?

Philippe