Re: GUM PRINTING QUESTION

Katharine,
As I can always predict, there is nothing I ever post that you
have found to corroborate in your gum practice, except for one thing that we
agree on--that using too hot water for a preshrink soak may interfere with
the sizing in a paper. I suspect I have misquoted that, too, but you'll
correct it I'm sure.

Let's go back to my story, and I am sticking with it:

1. A person asked if clearing was necessary.

2. A person also asked if colors faded with UV exposure once a gum print
was done.

3. I reported that in old literature, clearing was always optional. Sil
Horowitz concurs. I trust the old literature on quite a few things--not
all-- because at that time there were many gum practitioners, and therefore
a much larger body of experience to draw from than we have today.

I also reported that in old literature if a clear were felt to be necessary,
it was sometimes recommended to place the gum print out in the sun and it
would "clear" with sunlight. I couldn't believe this would be the case. I
tried it. It worked. I then tried it with both gum and albumen. I tried it
with no pigment. It worked the same every time.

This "clear" method was in a number of the old books. It wouldn't be a
recommended clear method because who wants to put prints in the sun anyway?
Still, it intrigued me.

I no longer clear anyway, and I no longer worry about NOT clearing, and I
don't worry about UV exposure on pigments once a gum print is done, within
reason (as long as I am using lightfast pigments, of course).

The fact that you got brown leads me to believe that you had remaining
unexposed and active dichromate in your paper. Maybe you didn't develop
long enough, who knows what could be your case. Whatever, this is not the
same situation I am talking about, nor does it relate, in my opinion, to the
original poster's question--does one need to clear? I assume the original
poster had developed his print long enough to remove any remaining active
dichromate from the paper.

I also know that the difficulty Mungo Ponton had with his dichromate only
exposed paper in 1839 is that the image faded to a pale green. It was not
permanent. From this ensued a number of methods in the early years of
dichromate printing to make this fading image remain, by adding different
chemicals or baths.

It stands to reason that active dichromate will brown to a considerable dark
brown in the sun. I did that, too, last summer, with dichromated gum left
in cups, both exposed and unexposed, both painted on paper and not painted
on paper, and with dark reaction and continuing action both, over a period
of a week, I observed a nice molasses brown occur.
Regards,
Chris

>> Katharine Thayer wrote:
>> >
>> > Chris,
>> > Well, I guess I'm confused, because I thought that in the issue of sun
>> > bleaching dichromate stain, you were talking about a brown (reduced)
>> > dichromate stain, not a yellow (unreduced) dichromate stain.
>>
>> Because if whatever it is that causes that rare bright yellow stain
>> (I've only seen it once or twice, when I was testing a lot of different
>> paper-sizing combinations) somehow arrests hexavalent chromium in the
>> hexavalent state and renders it stable (or at least unreducable) in that
>> state, that would be a rather remarkable finding.
>
>
> Curious, I tried to create a bright yellow dichromate stain (I've had an
> idea about what might cause this) but was able to create only a soft
> butter-yellow stain, not the bright yellow characteristic of hexavalent
> chromium (but still definitely yellow, not the tan or brown stain that
> is usually seen in gum practice). This yellow stain, after being
> developed half an hour and dried, did turn brown when placed outdoors
> half covered; the yellow was completely replaced with tan/brown in less
> than an hour. While there was no direct sun, there was enough UV to
> create a brown dichromate stain within two minutes on a (separate) sheet
> of paper coated with dichromated gum, that I placed beside the other one
> for a rough test of the available UV.
>
> The brown stain that resulted from the yellow stain being placed outside
> on a cloudy day didn't bleach within the four hours of remaining
> daylight.
>
> One test never proves anything, of course, but on the basis of this
> observation I wouldn't recommend that people assume that a yellow
> dichromate stain will stay yellow, or will lighten, when exposed to UV
> over time. My observation would suggest that yellow chromium can still
> be reduced to another form in the presence of UV, even when it is
> trapped within the sizing/paper as a stain, and even if the UV isn't in
> the form of direct sun.
>
>
> Katharine
>
Received on Thu Aug 11 10:57:46 2005