What is solarization?

[Sandy King <sanking@clemson.edu>]

Judy Seigel wrote:

I understand the term solarization as Cassell defines it, as a 
reversal that occurs from extreme over-exposure. For example, if you 
take a picture on a sunny day that includes the sun you will under 
some conditions get a reversal of tones, that is, the bright sun 
becomes a black circle.

Over-exposure of 2-3 stops does not constitute extreme over-exposure, 
at least in my opinion.

I don't know what to call the phenomenon that I observed and 
described but it does not seem to fit with my understanding of 
solarization, which would include halation, bronzing and gross 
reversal of tones.

Sandy



>On Thu, 9 May 2002, Sandy King wrote:
>>
>>  I think it is incorrect to describe the reduction in density that I
>>  reported as solarization. Solarization as I understand it is a gross
>>  reversal of tones. As I indicated in my first notes the difference
>>  between maximum density, which took place at about step 6 or 7, and
>>  the density at step 1, was on the order of log 0.05 to 0.10. I know
>>  because it was measured with a densitometer but visually you would
>>  been hard pressed to notice the difference. Carl Weese in an earlier
>>  message indicated that this was to be expected in Pt/Pd so there does
>>  not appear to be anything out of the ordinary here.
>
>What is the tipping point -- from "difference" to "gross reversal"? And
>if it isn't "solarization", what is it?
>
>For what it's worth, Cassell's defines "solarisation" as, "A term with
>many photographic meanings. It is synonymous with reversal (which see),
>and it is also applied to halation and bronzing."
>
>for Reversal: "REVERSAL OR SOLARISATION -- A phenomenon occurring as the
>result of extreme over-exposure, a positive instead of a negative image
>being produced on development. Abney has stated that preliminary exposure
>to diffused daylight, the use of a powerful developer, and the treatment
>of the plate with a solution of an oxidising agent before exposure,
>facilitate reversal; and, in his opinion it can only be produced when
>there is atmospheric oxidation. The addition of thiocarbamide to a
>well-restrained developer will produce reversal, especially if
>hydroquinone or eikonogen is used."
>
>All of which apparently refers to silver chemistry.  Whether or not the
>phenomenon in iron chemistry is same, similar, or other, is not (AFAIK) on
>record.
>
>Judy


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