UV density of base materials

banksy · Sep 18, 2009

Does anybody know what the UV density of Agfa copyjet is?

donbga · Sep 18, 2009

banksy said:
Does anybody know what the UV density of Agfa copyjet is?

I don't know about the Agfa product but I do know people use it for digital negs mage for UV printing.

Pictorico OHP is about 0.25 UV log density if I recall correctly. I think the copyjet material is similar.

Don

carioca · Sep 23, 2009

uv density...

banksy said:
Does anybody know what the UV density of Agfa copyjet is?

I think the question is not as simple as that.

There are more parameters involved:

-the light source you are using: BLB, TLK or other fluorescent UV tubes, metal halyde light sources, etc., for example.

-your contact frame glass: regular window glass, borosilicate or quartz glass, and the thickness of each, etc.? Each has a different UV-spectrum-blocking.

-the process you are working with.

All can cross-cut a general 'density' value definition for base substrates.

Sidney

donbga · Sep 23, 2009

Sidney said:
I think the question is not as simple as that.

There are more parameters involved:

-the light source you are using: BLB, TLK or other fluorescent UV tubes, metal halyde light sources, etc., for example.

-your contact frame glass: regular window glass, borosilicate or quartz glass, and the thickness of each, etc.? Each has a different UV-spectrum-blocking.

-the process you are working with.

All can cross-cut a general 'density' value definition for base substrates.

Sidney

Sidney,

None of the items you have listed above have anything to do with the applicability of the digital negative substrate.

Don Bryant

carioca · Sep 23, 2009

Don Bryant said:
Sidney,

None of the items you have listed above have anything to do with the applicability of the digital negative substrate.

Don Bryant

I appreciate the reply, but please explain.

Kind regards,

Sidney

donbga · Sep 23, 2009

Sidney said:
I appreciate the reply, but please explain.

Kind regards,

Sidney

What is there to explain?

Don

carioca · Sep 23, 2009

Don Bryant said:
What is there to explain?

Don

Ok, how do you measure UV density of a substrate?

S.

donbga · Sep 23, 2009

Sidney said:
Ok, how do you measure UV density of a substrate?

S.

Sidney,

One way is to use a UV densitometer.

Another is to use a step tablet and print the substrate lapped across the substrate on a sensitized paper using what ever UV light source you have, contact frame, etc. By inspecting the the resulting print you can see how much UV the substrate transmits or blocks.

If you change from one substrate to another all other things remain equal. What we look for in a substrate is sharpness, how well ink adheres and drys to it and how UV transparent it is.

For example Pictorico White Gloss Film is virtually opaque to UV light though it is quite sharp and holds ink well.

Don

Loris Medici · Sep 24, 2009

Don, it isn't as simple as you describe and I think that's what Sidney was trying to mention. See below:

UV densitometer says Pictorico base density is log 0.18 (something like 1/3 stop less than your 0.25 figure. BTW, I'm parroting Sandy King and Mark Nelson here - I don't have a UV densitometer myself...)

But when I do tests overlapping half of the step tablet with Pictorico, I get different results with different processes. For instance with pop Pd, Pictorico cuts 2 steps (in line with Sandy's and Mark's figures) whereas with traditional cyanotype the very same sheet cuts 3 steps! (More like your figure.) I haven't tried with gum but I'm sure it will be different for with gum too, *since each process is slightly different in terms of spectral sensitivity*.

So, UV densitometer measurements speak nothing to me. In my view, it should be specifically tested - unless one is 100% sure that their UV densitometer spectral sensitivity is very close to the spectral sensitivity of the tested process. But then you can't be sure w/o testing! So, banksy, make a test print anyway....

Regards,
Loris.

carioca · Sep 24, 2009

Don Bryant said:
Sidney,

One way is to use a UV densitometer.

Another is to use a step tablet and print the substrate lapped across the substrate on a sensitized paper using what ever UV light source you have, contact frame, etc. By inspecting the the resulting print you can see how much UV the substrate transmits or blocks.

If you change from one substrate to another all other things remain equal. What we look for in a substrate is sharpness, how well ink adheres and drys to it and how UV transparent it is.

For example Pictorico White Gloss Film is virtually opaque to UV light though it is quite sharp and holds ink well.

Don

Don,
the OP was looking for 'a density value' of the Copyjet substrate, my point was to show that a general value would not be of a big help.
I suppose he/she was looking for a comparision to some other substrate, in terms of exposure times.

By experiments with other members possessing UV capable densitometers, we have obtained different readings, simply because the spectral responses of the units used are not the same.
UV(A) light is not just UV light, it's a part of the spectrum between 315-400nm and each UV process has a different response to that spectrum.

Attached a spectral absorbtion curve reading of OHP (Pictorico) to give a practical explanation (this image has been posted a while back on this forum by a member, who's name I unfortunately do not recall) :

If my densitometer's response lies within the 310-330nm portion of this spectrum, my reading would not be very helpful to someone who is using a light source that mainly emitts in the 350nm area.

A higher or lower reading will not only influence the exposure time, but also have an impact on contrast, hence, a general value 'thrown out there' is not very accurate.

Best would be to experiment directly with the new substrate (keeping the same process setup), to get a precise comparision.

I hope I didn't make things more complicated as they are ;-)

Sidney

pschwart · Sep 24, 2009

Sidney said:
Don,
the OP was looking for 'a density value' of the Copyjet substrate, my point was to show that a general value would not be of a big help.
I suppose he/she was looking for a comparision to some other substrate, in terms of exposure times.

By experiments with other members possessing UV capable densitometers, we have obtained different readings, simply because the spectral responses of the units used are not the same.
UV(A) light is not just UV light, it's a part of the spectrum between 315-400nm and each UV process has a different response to that spectrum.

Attached a spectral absorbtion curve reading of OHP (Pictorico) to give a practical explanation (this image has been posted a while back on this forum by a member, who's name I unfortunately do not recall) :

If my densitometer's response lies within the 310-330nm portion of this spectrum, my reading would not be very helpful to someone who is using a light source that mainly emitts in the 350nm area.

A higher or lower reading will not only influence the exposure time, but also have an impact on contrast, hence, a general value 'thrown out there' is not very accurate.

Best would be to experiment directly with the new substrate (keeping the same process setup), to get a precise comparision.

I hope I didn't make things more complicated as they are ;-)

Sidney

One can skip taking UV measurements of the digital neg and just generate a correction curve by measuring reflection densities of test prints, but knowing the negative densities can streamline the process, especially when making significant changes (new printer, new ink set, new glop recipe, ...). I would say that the UV density of the substrate itself is probably the least useful value -- it's biggest impact will be on the base exposure required for dMax; no correction curve is required to determine that. It does indicate relative speed of substrates if everything else (printer, inkset, correction curve) is kept the same.

Loris Medici · Sep 25, 2009

pschwart said:
...
It does indicate relative speed of substrates if everything else (printer, inkset, correction curve) is kept the same.

Philip, relative speed of substrate is comparable only if the sensitizer formulation, ambient conditions and lightsource are the same. Printer, inkset and curve has nothing to do with it since speed is a function of sensitizer formulation, ambient conditions (= absolute water content of air for most processes), lightsource and base density (= negative substrate) - as I know it.

Regards,
Loris.

sanking · Sep 25, 2009

BTW, the UV base density of Pictorico varies quite a bit. Several years ago most of the Pictorico I used had a UV base density of about log .13, with some as high as log .18. The new regular Pictorico that I use today measured between .18 and .21, and the special Ultra version (which is designed to accept heavier ink deposits) measures log .27 - .28.

For any given set of conditions, i.e. same chemistry, same light source, , etc.) the base density is important because it determines how much exposure time is required to produce a maximum black (or maximum brown, blue, etc.). A substrate that has a base density of log .26 will print 2/3 of a stop slower than one with a base density of log 0.6. Again, this is when all other things are equal. And because of the self-masking we see with many processes the actual differnece in printing time may be even greater than 2/3 of a stop.

Sandy

Loris Medici · Sep 25, 2009

banksy said:
Does anybody know what the UV density of Agfa copyjet is?

banksy, in my tests it's 1 step (1/3 stop - it's a 31-step tablet) faster than original (old) Pictorico... Sorry for not being able to give an absolute figure, both because I don't have a UV densitometer and (as stated in messages above) it's only usable in a very limited / specific set of conditions... (Read as "it's non-usable" - according to me of course.)

banksy · Sep 25, 2009

Thank you all for taking the time to post - much appreciated.

pschwart · Sep 25, 2009

Loris Medici said:
banksy, in my tests it's 1 step (1/3 stop - it's a 31-step tablet) faster than original (old) Pictorico... Sorry for not being able to give an absolute figure, both because I don't have a UV densitometer and (as stated in messages above) it's only usable in a very limited / specific set of conditions... (Read as "it's non-usable" - according to me of course.)

Here are a couple of examples of when knowing the actual UV density of the substrate can be useful: after measuring the "old" and the "new" Pictorico OHP I was able to precisely calculate a base exposure for the new version. This also worked when I wanted to derive a base exposure for Canon TCF starting from OHP.

sanking · Sep 25, 2009

pschwart said:
Here are a couple of examples of when knowing the actual UV density of the substrate can be useful: after measuring the "old" and the "new" Pictorico OHP I was able to precisely calculate a base exposure for the new version. This also worked when I wanted to derive a base exposure for Canon TCF starting from OHP.

I make the same type of measurements and calculations as Phil. Also, after printing and drying a digital negative I always note the UV Dmin and Dmax to make sure that it fall in the DR I expect. Once I determine the DR of the negative I know how to sensitize the carbon tissue, or if working with pt/pd, how much restrainer to use.

Measuring UV density range is useful for both in-camera negatives and for digital negatives.

Sandy King

Shinnya · Sep 26, 2009

Hi,

I was in Tokyo a couple of weeks ago, and met people at Pictorico. They have something even more transparent film called TPW 100.

I do not have anything to measure with at my studio, but visually it is a lot more transparent. There is no milkiness at all. I am supposed to test to see it will take enough ink to make negatives.

If you want some samples, let me know. I can ask them to bring some more as I am meeting them again in NY and Philadelphia at the end of the next month.

They will be participating the PhotoExpo under Mitsubishi Imaging. If you got there, say hi to Yazawa-san and Eguchi-san at the booth and show your prints made with Pictorico. They will be happy to see how people take advantage of their product for creative needs.

Warmly,
Tsuyoshi

UV density of base materials

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