Re: Fog test. Was: Re: Making Digital Negatives (safelights for Pt)

Jeffrey D. Mathias (Jeffrey.D.Mathias@worldnet.att.net)
Wed, 29 Jan 1997 18:14:49 -0800

Tom Ferguson wrote:
...
> Standard Bostick and Sullivan chemicals, grade 5, half platinum, half
> palladium, on Cranes Platinotype paper.
...
Clearing was three 5 minute
baths in EDTA (3 teaspoons per liter of water).
...
> The problem with testing, is it always seems to show you something you
> didn't expect. Someone in this thread (Jeff ?) said that developing the
> paper with tape on it (to avoid getting chemicals on a section of the
> paper) was not only a way to test for safelight fogging, but if you
> developed a piece that hadn't been exposed to any light, it was a way to
> test if your clearing was complete. Unexposed paper in my situation does
> show a very slight "stain", compared to the "virgin" paper under the tape.
> I tried doubling my clearing time (three 10 minute baths), without any
> change.

Tom,
May I suggest you try the following to clear prints on Craines
platinotype paper.

A) place print in tap water for at least 5 minutes. (maybe 10)
B) place print through three 10 minute baths of H3PO4 (phosphoric acid,
reagent grade from chemical supplier), mixed 2 ounces acid in 1 gallon
water. I find that H3PO4 works best for clearing.
C) wash

or for step B:
B) place print through three 10 minute baths of HCl (hydrocloric acid),
mix 3 ounces of 20% muriatic acid (not the kind for swimming pools for
it has additives, but the kind found in hardware stores for etching
concrete.) into 1 gallon water.

EDTA DOES NOT CLEAR FOR ME. I have tried it, it does not clear. IT
DOES NOT WORK FOR ME. I do not want to hear from Richard Sullivan, it
does not work FOR ME.

Note: If you omit the tap water bath, I find that the B&S Crains
business card stock (special run) (what you call platinotype) takes an
hour to clear. For some magical, yet unknown reason the tap water bath
cuts the clearing time in about half. Try the test again and let me
know. I get no decernable stain when clearing this way.

Note: Other papers will clear differently with different times.

Note: A problem with HCl is that it will bleach the highlights. Oh,
you think you can give a little more exposure. Well, it seems that the
bleaching is non-linear (the highlights go first). This is especially a
problem for clearing times longer than 30 minutes total.

Note: Bad ferric oxalate will appear to give the same results as
staining or fogging. Check the ferric oxalate with the test I sent to
the list on Jan.14,1997 (RE: K3[Fe(C2O4)3].3H2O)

Thank you for your results on the cumulative exposure.

Jeff