U of S | Mailing List Archive | alt-photo-process-l | Mottling in lighter tones in cyanotype?

Mottling in lighter tones in cyanotype?

Hi. Trying to work out a last kink in cyanotype.

I am seeing mottling in my mid and light tones in both the image and an
exposed Stouffer step tablet.

I am using Arches Platine and a 1:1:2 Water:Sol'n A:Sol'n B cyanotype
emulsion (20gm/100ml ferric ammonium citrate, 8gm/100ml potassium

The Arches Platine has minimal runoff in the (inverted) wash I use.  I
am brush coating. I have rod coated also - but I seem to be seeing the
mottling regardless.

Ihave an exposure time to where I just merge the first two steps on a
31 step tablet.

Roughly some things I've tried:

	acidified and straight from tap wash water (my tap is alkaline)

	Tween 20 10% and none whatsoever (one drop per 60 drops

	Peroxide accelerate or not

I was working on a very low key print earlier and I was not seeing
mottling in the dark shadowed tones.

But I'm struggling here wondering if something slightly odd is
occurring suddenly.

My prep area is about 65 deg. F and 50% humidity.

I air dry the paper after coating for about one hour and use a hair
dryer to make it bone dry before exposure (in a glass vacuum frame).