[pure-silver] Re: B&W Positive from B&W Negative.
----- Original Message ----- From: <ellinger@xxxxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Tuesday, June 26, 2007 4:27 PM
Subject: [pure-silver] Re: B&W Positive from B&W Negative.



From:           "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
To:             <pure-silver@xxxxxxxxxxxxx>
Subject: [pure-silver] Re: B&W Positive from B&W Negative. 
Date sent:      Tue, 26 Jun 2007 14:52:53 -0700
Send reply to:  pure-silver@xxxxxxxxxxxxx
You can also make transparencies directly in the camera by reversal processing negative film. At one time Kodak had 
a kit for reversing T-Max but I don't know if its still
available. The reversal processs is well known but you have to experiment with the first developer. Another problem is 
that most 35mm B&W negative films have a pigment in the
support which is not removable. This cuts down the
brightness of the transparencies.
Adox Bluefire Police film has a very clear base. Not sure how it would be reversal 
processed though.

http://www.adox.net/Products.htm

Chris Ellinger
Ann Arbor, MI
USA
I think this is actually a microfilm and special developer. Microfilm might work well for slides provided one could control its contrast. Since projection transparencies need to be rather high contrast it might not be a problem at all. Note that the desired gamma for a transparency image is 1.0, that is, the same as the original scene. Since most B&W negatives are developed to a low value of gamma the positive film must have a value of perhaps 1.5 to 2.0 to yield the unity gamma. Usually the transparency is made slightly contrastier, perhaps 1.1, to compensate for flare in the projection system. Maybe not necessary with modern projection lenses. Some increase in density and some protection from fading can be had by toning, particularly in Selenium. due to the nature of the emulsion films may not tone change color much in the toner, probably desirable, but the toner will still intensify the blacks and give considerable protection to the image. 
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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