early 20th century glass plate iso

[thom_bennett]

I am researching an early 20th century photographer who used glass plates

and I got to wondering, what would the ISO of those glass plates be, stated in

today's terms? I don't think films were rated for speed then or were they? I am

simply amazed that photographers of that era got such wonderful portraits

with, what I am assuming to be, slow films. Thanks for your help.

[lex_jenkins]

Some glass plate emulsions must have been fast enough for handholding. I just received an e-mail from another photographer who has a 19th century Stirns "spy" camera disguised as a pocket watch that used glass plates 4cm in diameter. A scanned example photo, taken in bright sunlight, has no signs of motion blur from either subject or camera movement. The camera has no provision for tripod mounting and the subjects weren't posed - the photo is of women filling jugs from a public fountain, taken in Russia around 1895.

 

ISO 25 is more than fast enough for handheld daylight photography - any of us who've used Kodachrome 25 or similarly slow films know that. A glass plate emulsion with a speed equivalent to ISO 12 or even 6 would still be fast enough for handheld photography in bright sunlight.

 

Of course, there was no ISO standard back then but commercially made glass plate emulsions were consistent enough to enable well exposed photographs without guesswork.

 

According to some users who have experimented with Liquid Light for glass plate coating, it has an ISO of approximately 1/2 to 1 ISO. Perhaps Ron Mowrey will chip in some thoughts about speeds that might be possible with homebrewed emulsions.

[rowland_mowrey]

I have exposed current paper emulsions at ISO 25 including Ilford MGIV.

 

The current wisdom is that these are about 6 or 12, but when I center the picture in the middle of the tone scale and match it with a Polaroid of the same subject, I get 25. My highest speed home brew emulsion metered the same way gave an ISO of 200 (ortho sensitive), with some fog.

 

I would say that the average speed of mine, with everything under control and good ortho sensitivity will end up around 50. These will all be presented at my workshops in June and Sept (see the formulary of CFAAHP)

 

Kodak published an emulsion formula which is in the exposure range of 1/25th at f8. Go here: http://www.apug.org/forums/article.php?do=viewattachment&attachmentid=34

 

This document is a copy of the Kodak datasheet.

 

This yields an SRAD (Single Run Ammonia Digest) emulsion with some iodide in it. I have made one similar to it. It is fair for making in the home darkroom.

 

Ron Mowrey

[thom_bennett]

Thanks everyone for your responses; a great help!

[james_munoz]

Hello Thom

I do glass plates using the same process that was used in the 1850's and the ISO works out

to be something like 1-3 ASA.