Friday, July 31, 2009

Exposure of Liquid Light emulsion

What is the ISO or ASA or speed of Liquid Light emulsion? Well, I got a pretty good picture at f8 at 1 second on a almost brilliant sunny day of average subject. The Sunny Sixteen Rule was applied to those factors. As it turns out, a brilliant day is 200 or 20 depending on which light meter you use. It does not matter what ISO you have to work with; all meters and cameras and lenses are based on this Rule: brilliant sun is gaged at f 16 at 1 over the film speed for the shutter. So, if you have 200 as the bright sun as on a Weston light meter, and 400 for a film speed, f 16 falls on 1/400 second for exposure. Lenses must be focused on infinity. Anything closer will cause the bellows to be extended farther, decreasing light intensity by the square of the distance. Infinity focus is required to start with in order to determine exposure using the Sunny Sixteen Rule.

My daylight and exposure fit the above information perfectly. ISO was ... the lowest setting on any light meter at hand. Get a Weston 715 just for the dial, the cell does not even need to work. Light was 18.5 on a Luna Pro or one block lower than 200 on the Weston. It looks like I'll be using the old Weston meter again.

The other part of the equation is developing the exposed plate in the darkroom. This is also standardized. Dektol is used, diluted 1:3, one part Dektol to three parts water. Mix according to directions on the package to get the one part. One minuet is used as a time. 69 degrees Fahrenheit is the temperature throughout. Agitation is minimal. Kodak Fixer is used to both stop the development and to fix. A small amount of Fixer is put in a tray and used as a stop bath for 30 seconds. The fixer tray has more in it and is used for at least 2 minuets. If milky white is observed in the plate, then longer time is required to remove it. 5 minuets of wash in water is all that remains. Plates are stood on edge on a paper towel to dry. Drying can take one hour to all day depending on how thick the emulsion is, dryer air and more of it speeds things up. I place the completed dry plate in a sealable plastic bag.

Washing comes first, Calcium Carbonate or Barkeeper's Friend are enough with a tap water rinse to get the emulsion to stick. I scrub the powder with a brush and a little bit of water over the plate in a tiny tray. Lots of tap water cleans it off. That is all that is needed.