Topic: Glass plate negs - advice on iso rating

[Janet_P]

Hello, I've just bought some glass plate negs for my rollei's plate adapter (oh joy  ).
Would you say that the Ilford N.25 and N.40 plates I bought are likely to be 25 and 40asa? Because they're so old I'll obviously have to downrate them anyway. Any ideas what too?

All ideas and suggestions greatly appreciated.

Cheers
Janet

[Andrea.]

So it was you!
Rate them low - about 6 asa or so should do it. At least that's what i have done.
quite pften there is an info sheet in the box with a receipe on - developer that is. I tend to use anything i have to hand :-0

[Francois]

I don't know if you have many but here's an idea of some sort.
I'm not convinced 100% but... here I go.
Make some sort of cardboard mask that fits in front of the plate. Put it all in the camera and make some sort of test strip.
Making pictures of an 18% gray card would ensure an easy to calibrate target.

I don't know if it makes any sense...

Or you could do the test strip under the enlarger (same time, different exposures) end measure the enlarger's output with a regular lightmeter...

That's probably what I would do if stuck...

Good luck on finding the right ISO... but it's probably quite low like Andrea said.

Come to think about it, are they ortho?
If so, you could expose approximately and process by inspection...

[Janet_P]

Oops sorry Andrea  didn't mean to outbid a fellow filmwaster - especially one who's subbed me before.

Thanks for the advice. I'm going to do some tests and I'll let you know how it goes.

Janet

[Francois]

Hi Janet!

I just came across this by total accident and I thought you might find it interesting.
It's an extract of the G.Cramer Dry Plate Company's publication aptly titled: Cramer's manual on negative making and formulas, 20th edition.

Lets just say it's very old... their prices say that 4x5 plates are sold at 0.80$ per dozen... 30 dozens per case...
I somehow wish these prices were still in effect

Anyways, here's the extract:

To try the speed of the plate and ascertain the correct exposure.
I t is advisable to make a test by exposing three plates, one rather short, the second twice and the third three times as much time, and compare the manner in which the image appears during development.
In an underexposed plate it will take longer for the image to appear and there will be lack of detail in the shadows.
Overexposed plates show full detail but lack contrast; prolonged development will increase the contrast as well as the density.