Glass negs

[dwross]

So, what ISO would home made dry plates be? I've heard they are about ISO 1.0, or ISO 0.5?
Kent in SD

Oh, heavens, no. At the 45th parallel, this recipe

http://www.thelightfarm.com/cgi-bin/htmlgen.py?content=30Dec2011

gets 6 to 40, depending on time of year and time of day, and to a lesser extent, altitude. (It is impossible to place a single ISO number on anything but panchromatic films. If you read otherwise, this is a red flag to suspect the experience of the source.)

d

 

[Two23]

Oh, heavens, no. At the 45th parallel, this recipe


gets 6 to 40, depending on time of year and time of day, and to a lesser extent, altitude. (It is impossible to place a single ISO number on anything but panchromatic films. .)

d

How on earth can I shoot with a "film" if I don't know what the ISO is? The range 6-40 is about three stops! It would take a serious investment in time to get a shot off, and then the exposure is a crap shoot. Are the panchromatic plate emulsions more predicitible?


Kent in SD

 

[MattKing]

Kent:

The non-panchromatic films are like the old tungsten films - they have different sensitivities depending on the colour temperature of the light.

So you need to know those sensitivities, and the colour temperature of the prevailing light, in order to accurately determine exposure.

 

[Hexavalent]

How on earth can I shoot with a "film" if I don't know what the ISO is? The range 6-40 is about three stops! It would take a serious investment in time to get a shot off, and then the exposure is a crap shoot..

Welcome to the world of colourblind emulsion; patience and perseverance required!

 

[EASmithV]

just pull out the darkslide while doing a sunny 16 test. it's just like a test strip. I did this to find out that liquid light is approximately ISO 0.50 to 0.75

 

[premortho]

There were speed ratings as far back as the '90's...and not the 1990's either. I still use Ortho film mostly in large format. I used to use super plenechrome press and super speed ortho, super speed ortho was rated at about 125. BUT, in the lovely little papers that came with it it gave all the modifiers for filters timr of day, and time of year. 125 speed was for a bright sunny day, between 10:00am and 3:00pm, in the summertime. Shooting snow scenes early or late day could slow down to asa 10.

Oh, heavens, no. At the 45th parallel, this recipe

http://www.thelightfarm.com/cgi-bin/htmlgen.py?content=30Dec2011

gets 6 to 40, depending on time of year and time of day, and to a lesser extent, altitude. (It is impossible to place a single ISO number on anything but panchromatic films. If you read otherwise, this is a red flag to suspect the experience of the source.)

d

 

[dwross]

Thanks for posting that info. Very interesting! It tracks perfectly with my latest experiences. When I posted "6 to 40", I hadn't stumbled on salt-into-silver precipitation ("normal" historic emulsion making has it as silver-into-salt). That's made a Universe of difference in speed. The take home message for me is that all the limitations we think (or have been told) exist to making our own materials are probably wrong. Dream it; make it (only caveat: still a lot of work.)

 

[Marizu]

Regarding (wetplate) collodion, why exactly does one have to shoot immediately? What if you vacuum sealed it on the spot while coating? Curious if it'd be possible to make collodion plates that you could, you know, unwrap and use on the fly.

They are no longer light sensitive when they are dry. Any previously exposed latent image disappears if the plate dries out.

The collodion is like a thin coating of syrup with a thin film and nothing can be in contact with it or it will impact the image.

There was an old technique of covering a sensitised plate with honey to stop it evaporating.
This honey process meant that the plate could be transported for several days.