Re: Gum image has reversed

Thanks to everyone for their quick and helpful responses. If anyone is
interested, I have posted a copy of my problem on this page:

http://www3.telus.net/pollock/gumdemo1.htm

I have taken a number of lessons from your advice:

(1) size the paper first
(2) cut way back on the pigment level
(3) try a different pigment altogether
(4) watch the exposure time

Here are a few other thoughts and replies to some of the other comments:

Humidity -- I live on the wet west coast of Canada where we have been
experiencing what we call the "Pineapple Express" series of winter storms
from Hawaii. I have no idea what the technical humidty level is at the
moment, but let's just say that the birds are swimming, not flying.

Exposure -- I started out trying to use my 4x5 enlarger with a Cold Light
Head as a light source. I think (not sure) that is should be a good source
of UV, but it's just not intense enough. I gave up on that and followed the
lead of Katharine (your web site is an invaluable resource) and tried my #2
photoflood. I found that I had to get my exposures up into the 20 minute
range in order to get anything at all. Anything in the 6 to 12 minute range
resulted in the gum just washing away. What I was trying to do was follow
the standard approach for making a silver gelatine print, i.e. find the
minimum exposure time which will give you maximum black in the unexposed
areas of a negative. That lead me to the 20 minute exposures. However,
given the advice on overloading my gum with too much pigment, I will try to
scale back my exposure times as I scale back my pigment.

Other reasons for reversal of images -- I'm not sure whether this is
relevent to printing with gum, but severe overexposure using silver
materials will reverse the tonality. Ansel Adams demonstrated this with an
image on one of his Basic Photo Series books. In a shot of the setting sun,
the sun itself has turned black (in the positive final print) because of its
severe overexposure in the negative. The rest of the image looks normal.

Thanks again for the advice. I'm out of town for the next few days and
won't be able to put it into action until the weekend. Stay tuned.

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Monday, January 09, 2006 10:14 AM
Subject: Re: Gum image has reversed

>A couple more comments about "tonal inversion":
>
> To say it's somehow related to exposure is to say the obvious, as the
> whole inversion thing requires different levels of exosure to be present.
> With no exposure, the entire paper would be stained, rather than there
> being a reverse image, which sort of goes without saying. But it also
> doesn't make sense to say that it's caused by underexposure, because
> underexposure can't cause a reversal image unless the gum is overloaded
> with pigment to start with. And if there is excess pigment present,
> exposing more won't make the problem go away, as is shown by the partial
> inversion on the "for fun" page I showed the other day:
>
> http://www.pacifier.com/~kthayer/html/tricolorfun.html
>
>
> where the image is correctly exposed, but is still partially reversed as
> the result of overpigmentation.
>
> For a complete reversal of tones, where what should be the darkest tones
> are the lightest, the bulk of the emulsion has to have left from the
> areas of greatest exposure, one way or another. This leaving of the
> emulsion can happen as a result of underexposure, but it can also happen
> as a result of flaking off of the pigment, as a result of severe
> overpigmentation resulting in a too thick layer, or from printing on a
> hard surface resulting in the floating away of the hardened gum, as in
> the experiments on glass some of us were doing a couple of weeks ago.
>
> Tonal inversion will occur on well-sized papers; it isn't a question of
> sizing or not sizing. It's all about pigmentation, how much pigment a
> particular gum can hold in suspension. If you're not getting staining or
> inversions, your pigment loads are no doubt well within the capacity of
> the gum. I don't think it's useful to make characterizations about the
> amount of pigment we use in ordinal terms, because we all mean different
> things by those terms. For example, some time back, Chris said she uses a
> huge amount of pigment, and gave the amount of pthalo she uses as an
> example. Curious, I figured out how much pthalo I use, and found that we
> used the same amount of pthalo paint as a percentage of total emulsion,
> although when I talk about how much pthalo paint I use, I say I use a
> very small amount, since it's so much less than I use of many other
> pigments. My point is that it wouldn't be very useful to assume that
> because Chris says she uses a lot of pigment and I say I don't use very
> much pigment, that means Chris uses more pigment than I do. My feeling
> about this whole pigment concentration issue is that gum knows how much
> pigment it can hold, and will let you know if you've given it more than
> it can carry, and that all of us who successfully print gum are probably
> using about the same amount of a given pigment, regardless of the label
> we give to that amount.
> Katharine
>
>
>
> On Jan 8, 2006, at 8:56 PM, Katharine Thayer wrote:
>
>> Hi Bruce,
>> 1. The negative image, in my opinion, is the result of too much pigment.
>> There's been some discussion of this fairly recently (in the last two
>> months) on this list. Not everyone agrees with me about this, but I'll
>> bet if you'll cut back on your pigment, you'll get a positive image.
>> The reason it's black where there should be white, or light tones, is
>> pigment stain, and the reason it's white where it should be black is
>> that the emulsion was so thick (pigment- laden) that it flaked off.
>>
>> 2. I don't know what to say about your gum. I don't know the current
>> Photographer's Formulary gum, although I loved an earlier version. I
>> think the two problems are related to pigment concentration; with a
>> heavy (but not overly pigmented) pigment load, you will get a high
>> contrast image. It looks like with one gum (the prepared gum) you're
>> just under the limit for the amount of pigment that the gum will hold in
>> suspension, and with the other one, you're just over the limit and
>> that's why you got the inverted image.
>> Katharine Thayer
>>
>>
>> On Jan 8, 2006, at 8:40 PM, Bruce Pollock wrote:
>>
>>
>>> I'm new to the list and will apologize in advance for the barrage of
>>> questions which I'm going to unleash over the next little while. My
>>> frustration level is running quite high. However, for the moment, I
>>> will try to limit myself to two main problems.
>>>
>>> First, a little background. I dabbled in gum dichromate about 25+
>>> years ago and had some satisfactory results, but never really stayed
>>> with it. I always wanted to get back into it and so, here I am. I
>>> still have the 1 lb. jar of Potassium Dichromate I bought back then and
>>> still have some Gum powder as well. Whether the age of my chemistry
>>> has any bearing on the results I've experienced, I'm not sure. I
>>> really can't see how Pot Dichr can "go bad" but, you never know.
>>>
>>> My first question relates to the first usable print I've obtained after
>>> many, many failures. I finally have something that suggests I have a
>>> chance of success, but the print has reversed to negative. Can anyone
>>> explain this? The detail is quite good, but I have a negative, not a
>>> positive. Here are some details about my method:
>>>
>>>
>>>
>>>> Lanaquarelle Medium Watercolour 140 lb. Paper, *not* sized
>>>> Analogue 4x5 negative made in-camera on Tri-X film
>>>> #2 blue photoflood light source about 25 inches from neg
>>>> 20 minute exposure
>>>> Emulsion made from 2.5 ml gum, 2.5 ml potassium dichromate solution
>>>> and about 0.5 gm Daniel Smith Lamp Black pigment
>>>> Still development for about 10 minutes brought up reasonable
>>>> density -- my fear in letting in go on much longer was that I'd loose
>>>> the entire image (just like the first dozen or so failures).
>>>>
>>>>
>>>
>>> I realize that I should probably size the paper and that Lamp Black is
>>> not the best starting pigment, but I was just trying to get myself into
>>> the ball park on emulsion and exposure times. However, I'm stumped by
>>> the negative product.
>>>
>>> My second question relates to the type of gum arabic I should be using.
>>> This success (if you can call a negative print a success) came after I
>>> switched back to my old gum arabic powder (25+ years old). The gum was
>>> a fine, white powder which I put into solution using the formula in
>>> "The Keepers of Light" by William Crawford. My earlier failures had
>>> been done using some Gum Arabic pre-mixed solution recently purchased
>>> from Photographers Formulary. Using the pre-mix I got virtually no
>>> results -- anything I got was basically a "soot and chalk" type print
>>> where the shadows went black and the highlights blew out. Nothing in
>>> between. No detail at all.
>>>
>>> Can anyone explain the lack of results with the pre-mix Gum Arabic?
>>> Should I stick with the powdered form and mix it myself? The fact that
>>> I got *some* results from the powder suggests to me that the pre-mix is
>>> somehow at the root of my earlier problems where I got soot and chalk.
>>>
>>> Many thanks in advance -- all advice gratefully received.
>>>
>>> Bruce Pollock
>>>
>>>
>>>
>>>
>>
>>
>
>
Received on Mon Jan 9 20:49:03 2006