Fibre RA4

[Photo Engineer]

To continue with baryta vs non-baryta papers, one must consider all of the above.

Baryta papers are heavily calendered with tons of pressure applied to the surface of the barium layer. This makes the baryta layer less permeable than the fibres of plain paper and is relatively independant of the presence or absence of a gelatin subbing layer.

You might say that in order of permeability, RC is impermeable, Baryta is more permeable, and plain paper is very permeable. Again, this is not dependant on whether there is a subbing layer present on any of these supports.

In addition, the baryta layer contains humectants and is loaded with the baryta itself. Regular paper is just a fibre substrate. Therefore, when I coat on plain paper vs a baryta paper, I see a big difference in repellancy. I also see what appears to be a difference in equillibration of chemistry somewhat like coating on RC, in other words, the baryta is between plain paper and RC in terms of reequillibration of chemicals and diffusion of chemicals and water. Within about 10 minutes though, the back of the baryta paper is as damp as the plain paper. It is initially more repellant!

This is all tied together with the emulsion formula. If a given emulsion is adjusted to a given pAg with salt and then surfactant is added, it may coat well on plain FB, but not on baryta FB. You may need to change either the salt level or the surfactant or both. If the salt is changed, then the emulsion is changed. The surfactant only needs to be changed if the repellancy can be cured by this method, but the salt level must be changed if salt diffusion or stabilzer diffusion become important.

Again, nothing is simple and this is why it is an art as well as a science.

PE

 

[Ryuji]

You might say that in order of permeability, RC is impermeable, Baryta is more permeable, and plain paper is very permeable. Again, this is not dependant on whether there is a subbing layer present on any of these supports.

I wouldn't say that. Your discussion is missing one huge subject: internal sizing of the paper. There are a huge rage of paper stocks available for photography, watercolor, printmaking and other applications. One very important aspect of the difference is that they are adjusted to different degree of hydrophilicity of cellulose by using suitable kind and amount of internal sizing agent.

Selected from non-baryta variety, I find papers that are most suitable for silver-gelatin photography are internally sized with dimeric alkylketene derivatives, stabilized by starch derivatives, and most preferrably, additionally surface sized with gelatin blend containing at least 20% trimellitiaged gelatin, or at least 30% phthalated gelatin, hardened with usual hardeners like vinylsulfones, active halogens, s-triazines, epoxides, glutaraldehyde, etc. These papers are only modestly absorbent and exhibit very good adhesion as well as wet strength. They also dry fast and flat as a fiber paper. These papers are inexpensively available in variety of sizes and surface textures.

 

[Photo Engineer]

Ryuji;

Any given paper, whatever interal characteristics, becomes less permeable when overcoated with baryta and calendered. The internal characteristics become more evident as the paper becomes wet after coating. So, the generalization stands with respect to order of permeability with the various barytas falling within the center of the range. The family of plain fiber based papers falls on the higher side of permeability as I stated previously.

However, since the other readers don't care about all of the chemistry expounded above, I won't restort to any of that. I'll just recommend a family of plain papers and baryta papers to those who wish to duplicate my work. This includes the formulas to coat on them. This will be available, with detailed instructions and formulas.

I have stated elsewhere that a good point to start is Strathmore Smooth right out of the package with no extra preparation. This is what was used for the 8x10 print sample that I posted in another thread. I think that naming a good paper is better than citing a bunch of chemical names. Posting the example is the next best thing. I've done both.

I think that is enough.

PE