fotospeed gum bichromate kit + a few questions
i'm on my first foray into gum printing, using the fotospeed kit.
has anybody ever used this kit? and has any tips or bewares for using it?
one thing i'm wondering is that there's not a single word on the dangers of gum printing. it's not even mentioned which chemicals are in the solutions.
so, the sizing should be some kind of gelatine- harmless (although smells horrible). so is the gum arabic.
the sensitizer is potassium or ammonium dichromate - the dangerous stuff.
but what's in the clearing solution?
and the exposure?
the fotospeed manual says: up to 24minutes for sunlight; bill mabrey says: 6-7minutes in sunlight.
and does it have to in direct sunlight or is normal daylight sufficient (not in the shadows of course)?
if i coat the paper today (at night) and plan to do the exposure tomorrow afternoon, is it safe to store the dried, coated paper? say, in a bag which comes with photographic paper?
and how to store the developed gum prints? is all the bichromate gone after development (the water bath)?? or are there still traces of the chemical in the emulsion?
i somehow don't trust those images...
Last edited by phritz phantom; 08-27-2007 at 06:33 PM. Click to view previous post history.
I've never seen this kit, but it sounds from your description as though nothing is labeled by its real name, is that correct? Surely there must be instructions with it that tell you what things are... If not, shame on them.
If the sizing comes premixed, it's not likely to be gelatin with a hardener; who knows what it is, if they don't say.
The clearing agent is most probably sodium bisulfite or potassium metabisulfite; they are equally effective clearing agents. (There's a thread somewhere in this forum about that.) They give off fumes that can make you cough, so you should use it in a well-ventilated place, but other than that it's not too terrible.
Exposure in sunlight depends on the strength of the sunlight (it's widely variable depending on location, season, and time of day) and the strength of the dichromate. With saturated ammonium dichromate, I usually figure my times in direct sunlight in seconds rather than minutes (in other words, less than a minute.) Indirect sunlight also has a lot of UV, and I've exposed prints in 3 minutes or so even in the shade, but my experience is that indirect light tends to make the image more diffuse (small details can turn into blobs rather than printing sharp) since the radiation is coming from everywhere rather than from one place.
Gum printing really isn't all that dangerous. The only thing that's "dangerous" is the dichromate, as you say, and it's really only dangerous in industrial quantities, especially when breathed; it caused cancers of the breathing passages in people who had to spray it onto car bumpers, back in the days when car bumpers had a chrome finish. In the small quantities we use it in, it's really fairly harmless. I wouldn't recommend eating it, and some people caution that you should use a mask when weighing the powder, though I never do, and some people develop a contact dermatitis from putting their hands in dichromate-laced water, so it would be sensible to wear rubber gloves just as a precaution, though I never have.
The issue about keeping coated paper overnight is the dark reaction, which is a reaction between the gum and the dichromate that starts when the two are mixed and coated into a film, and proceeds even in complete darkness. But the speed of this reaction is highly dependent on humidity (and is also influenced by other things such as dichromate concentration); In a very dry environment the reaction proceeds so slowly that its effect is negligible and people can leave their coated papers even for weeks without fogging; in very damp environments the reaction proceeds rapidly enough that it wouldn't be advisable to leave paper overnight, or even for a couple of hours. So it depends mostly on the humidity.
A finished gum print should be quite inert and archival, if permanent pigments are used. The unreduced dichromate leaves the paper right away in development; there's not likely to be any left in the print after development.
thanks for the lengthy reply. you answered all my questions... and a few ones more.
yes, there are instructions included with the kit, they seem to be quite detailed and accurate. but, as i said, what i found to be strange, was that there's not one single word on the chemicals included.
all bottles are labeled with names, but those names are only "sensitizer" or "sizing solution",...
so i don't even know if my sensitizer is potassium or ammonium dichromate.
i just coated my first sheet (doesn't look that good, i have to confess) and will try exposing for 3 minutes tomorrow afternoon.
and i will take a big look at your page asap.
Last edited by phritz phantom; 08-27-2007 at 08:08 PM. Click to view previous post history.
ok, now my first try was a failure.
i could see a very faint image, but even after about two hours in a waterbath - tried everything: soaking, running water, brushes and even gentle rubbing - nothing changed. the image became even more faint. i also never saw any flakes come off, the image stayed the same pretty much.
i think the reason is because my emulsion is too thin. i expected the emulsion to have a consistency more like honey than normal watercolor. the emulsion i brewed was definitely more like watercolor and so was its color (a little uneven and not very opaque).
i used 5ml gum solution and 5ml of sensitizer + a less than pea size portion of pigment for a 15x15cm image (appr. 6x6inch).
should i use more pigment the next time?
i wonder, if the image was severely underexposed - i only exposed for 4,5 minutes on a sunny day, instead of 24min said in the fotospeed kit manual - wouldn't all of the emulsion come off?
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Originally Posted by phritz phantom
one more question:
how thick is your layer of emulsion? can you still see the paper through or is it completely opaque?
sorry, about stealing your time with all that questions.
thanks once more. and great homepage. very informative.
No problem; I enjoy doing what I can to help people who are struggling with gum.
Originally Posted by phritz phantom
I'm really curious about your sensitizer, what type and concentration it is, if the kit instructions recommend a 24-minute exposure in direct sun. That's awfully long, for gum even with saturated potassium dichromate, so I wonder if they've diluted it. Did it come premixed?
My layers really vary depending on what look I'm after. If I'm doing a one-coat gum with a dark DMax, or a dark layer to fill in just the deepest shadows on a multicoat gum, then chances are the coating will be heavy enough to look completely opaque as it's brushed on. Otherwise, my layers tend to be more transparent. Some gum teachers teach that the layer should be thin enough that you should be able to read text through it, if you coated it on a newspaper page, and I think that's fairly good advice to keep beginners from overpigmenting, but I don't look at it as a hard and fast rule.
A less than pea-sized ball of pigment in 10 ml of gum/dichromate isn't excessive at all (to make the heavy, stiff emulsion of iron oxide black that I described in a thread on black pigments, I emptied an entire tube of paint into 15 ml gum) and if it's a weak pigment or a chintzy brand, might be less than adequate. It's really impossible to give a general rule about this.
Not sure any of this is as helpful as just varying the variables one at a time (exposure, pigment load, etc) and seeing for yourself what happens. But feel free to continue to ask questions as you go along.
i really can't say anything about the sensitizer. also nothing on the fotospeed hp: no datasheet etc. i can only say that's an orange liquid (with a little bit residue on the bottom) and they recommend mixing it 1+1 with the gum solution. and yes, everything was pre-mixed.
there seems to be something fundamentally wrong with the emulsion. there is only one pigment included (looks like i got the cheap version of the kit), which is "payne's grey". it did look grey - in dim light - when i painted it on, but turned blue after exposure and a long, long time of washing.
i will size and pre-shrink a few more papers today and will try again tomorrow, without the over-night storage period.
hopefully, because the weather forecast isn't too good...!
Don't give up yet! There's probably nothing wrong with the materials; you just need to figure out how this particular combination of materials works together. If the instructions say 24 minutes in the sun, then the sensitizer must be diluted enough to make that a reasonable exposure, and I'd follow the instructions.
Originally Posted by phritz phantom
Payne's grey is an interesting choice for a kit. Monochrome kits always used to use lamp black, but that's a difficult pigment for beginners to use without staining, and I suppose Payne's grey seemed safer. It's not a specific pigment in itself, but a convenience mixture of black and blue. Most manufacturers use lamp black for the mixture, but they use different blues.