altered dektol

["Gordon J. Holtslander" <holtsg@duke.usask.ca>]

Hi:

I did some fiddling around in the darkroom seeing if I could turn dektol
into a low-contrast developer suitable for making high contrast ortho film
behave like a standard continuous tone film.

I've had pretty good success.  I used Kodak Camera 2000 CGP ortho film and
started with standard dektol.  As a test subject I contact printed a
fairly contrasty tri-x negative with lots of highlight and shadow detail
- a picture of the falls in Johnston Canyon in Banff.

I started by adding baking soda to straight dektol.  This produces a lower
contast image, but is too contrasty for an interpostitive.  It may work
for producing pinhole negatives from a very low contrast scene.

Increasing the volume of baking soda decreases the contrast up to a
certain point, after which additional baking soda does not change the
contrast - it just clumps in the bottom of the tray.

Next I tried adding small volumes of stop bath to the developer.
This decreased the contrast some, but not to the same extent as baking
soda.

I had best success with baking powder.  My understanding of baking powder
is that it is supposed to produce carbon dioxide when added to water.  It
does this by having a mixture of sodium bicaarbonate and some other
chemical(s) to produce a slightly acidic solution so that the sodium
bicarbonate dissociates to produce carbon dioxide.

The same slightly acidic environment is needed to slow the activity of the
developer to turn it into a low contrast developer.

I used "Magic Baking Powder" a Nabisco product.  Its ingredients are (in
order)

corn starch
monocalcium phosphate
sodium bicarbonate

I diluted the dektol 1:1 with water

100 ml dektol
100 ml water.

I then added two teaspsoons of baking powder.  The developer turned
white and fizzed.  There was a powdery suspension in the developer - I
assumed it was the corn starch.

This produced an image with similar contrast to the baking soda + dektol.

I added another two teaspoons of baking powder. (total of 4 teaspoons
baking powder) This produced an image with even lower contrast.  There was
also a distinct loss in film speed.  This was even lower contrast than the
previous but still too contrasty.

I added another 2 teaspoons of baking powder and increased the exposure
1/2 stop.  this gave a good low contrast image but still underexposed.

I did a proper test strip.  All the initial test exposures were 10 seconds
long. The correct exposure for the developer now was 60 seconds.

I exposed another test for 60 seconds and developed it for 3 minutes.
(All previous test were developed for one minute)

I was able to get an image with very good shadow details in the dark rocks
of the image and still hold all the highlight details in the water
cascading over the falls.

So far good success with:

100 mls Dektol
100 mls water
6 teaspoons Magic Baking Powder

To produuce "normal" contrast images using high-contrast ortho film.

Gord

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Gordon J. Holtslander		Dept. of Biology
holtsg@duke.usask.ca		112 Science Place
http://duke.usask.ca/~holtsg	University of Saskatchewan
Tel (306) 966-4433		Saskatoon, Saskatchewan
Fax (306) 966-4461		Canada  S7N 5E2
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