Add part of Color Image Superposition (sic) section. No compile.

NOTES_ON_OPTICAL_PRINTER_TECHNIQUE.md

@@ -908,29 +908,35 @@ Pressing one eyeball produces such superpositions.
 
 ## FLASHING
 
-Double exposing an image with no image -- sere light -- lightens
-(or with colored light and color print filma, colors) the blacks
-and darker tones while having little effect on middle tones
-and even lese on lights. It is8 not a true method of contrast
-reduction.
+Double exposing an image with no image--mere light--lightens (or with colored light and color print films, colors) the blacks and darker tones while having little effect on middle tones and even less on lights.
+It is not a true method of contrast reduction.
 
-Sepia toning can be simulated by both color flashing and color
-filtering when printing B&W original onto color reversal print filr
-A healthy yellow, magenta, or cyan flash when printing onto color
-reversal film yields, respectively, the yellow, magenta, or cyan ~
-image, as if this dye layer were prised from the original film.
-There ie no photographic method for unflashing a flashed image.
-There is image addition (double exposure} and image pultipliocation
-(Dipack) and even image division (bipack of positive with
-negative), but no image subtraction.
+Sepia toning can be simulated by both color flashing and color filtering when printing B&W original onto color reversal print film.
 
-CONTRAST ADJUSTMENT Gammas add or subtract in a bipack, so bipacking
+A healthy yellow, magenta, or cyan flash when printing onto color reversal film yields, respectively, the yellow, magenta, or cyan image, as if this dye layer were prised from the original film.
 
-can adjust contrast. A bipack (printed gamma 1 or
-Viewed raw) of an original with its duplicate is
-like a double contrast original. <A bipack of an
-original with its low contrast negative is like
+There is no photographic method for unflashing a flashed image.
+There is image addition (double exposure) and image multiplication (bipack) and even image division (bipack of positive with negative), but no image subtraction.
 
-~ a darkened reduced contrast original.
-“fhe bipack of an original with ite high contrast
-negative is like a Sabattier solarization!
+## CONTRAST ADJUSTMENT
+
+Gammas add or subtract in a bipack, so bipacking can adjust contrast. A bipack (printed gamma 1 or viewed raw) of an original with its duplicate is like a double contrast original.
+A bipack of an original with its low contrast negative is like a darkened reduced contrast original.
+
+The bipack of an original with its high contrast negative is like a Sabattier solarization!
+
+## COLOR IMAGE SUPERPOSITION
+
+There are the same three basic types.
+
+Double exposure from positives gives additive color mixture.
+Bipacking gives so-called subtractive color mixture.
+When bipacking color negatives the extra orange mask should be neutralized by filtering.)
+
+Double exposure from negatives gives something else.
+
+For greys in the two images, combination is as for B&W.
+But for colors, not only are new colors produced but apparent brightnesses do not combine quite the same ae for B&W.
+
+The dyes in Wratten CC filters Y, M, C are similar to those in color films.
+Film colors can be simulated by packs of these filters and much can be learned about film color manipulation from familiarity with the filters and their combinations.