How multigrade paper works

[Young He]

Hello all,

I am somewhat curious about how multigrade paper works. I am aware that the paper uses two different emulsions with different sensitivities and contrasts mixed together or coated in a multilayer. However, is it possible to make a rudimentary multigrade paper with two emulsions that are the same contrast and are only sensitized to different wavelengths?

 

[NedL]

Often three kinds of emulsions. This document explains it pretty well.

I think the theoretical answer to your question is "yes", but in practice it is difficult to make an emulsion that is not sensitive to blue and UV. So in practice, the different emulsions that make up multigrade paper instead have differing sensitivities to longer wavelengths of light. Then the curves are "tuned" so that the contrast transition is reasonably smooth.

 

[AgX]

However, is it possible to make a rudimentary multigrade paper with two emulsions that are the same contrast and are only sensitized to different wavelengths?

No.

 

[MattKing]

The two (or more) emulsions have the same contrast.
They have different speeds, and contrast is controlled and achieved by adding their respective built densities.
Read about it in Mr. Lindan's excellent article from his Darkroom Automation site: http://www.darkroomautomation.com/support/appnotevcworkings.pdf

 

[Young He]

Ok. Thank you for the information.

 

[AgX]

There have been made most different approaches to yield a variable contrast paper.
My answer was "no", as I assumed the average reader would understand with "same contrast" something different than finally applied by Ilford.
The author of the linked dokument is erronous or at least misleading in a major point.

 

[john_s]

This might help:

http://www.darkroomautomation.com/support/index.htm

and choose The Workings of Variable Contrast Papers and the Concept of Local Gamma

 

[twelvetone12]

The author of the linked dokument is erronous or at least misleading in a major point.

which point? (no polemic, I'm genuinely interested)

 

[RalphLambrecht]

Hello all,

I am somewhat curious about how multigrade paper works. I am aware that the paper uses two different emulsions with different sensitivities and contrasts mixed together or coated in a multilayer. However, is it possible to make a rudimentary multigrade paper with two emulsions that are the same contrast and are only sensitized to different wavelengths?

let's leave that for PE to answer.

 

[AgX]

which point? (no polemic, I'm genuinely interested)

There is a 80 years history to contrast variable materials. And Ilford themselves started with two emulsions of different contrast. Only recently, with type 4 they changed that.

 

[RauschenOderKorn]

I thinks the question has been answered already here:

https://www.photrio.com/forum/threa...rs-with-emulsion-coating.110745/#post-2017016

 

[jvo]

it's done with precise mix of pixie dust, shamanism, and enchantment.