Re: digital negative possibilities for gum
On Oct 16, 2006, at 8:07 PM, Katharine Thayer wrote:
Chris, what kind of bitmaps were you using, a halftone screen,
diffusion dither, or some other?
The reason I'm asking is that I'm not sure what it is you're
comparing when you're comparing a negative made by printing the file
as a bitmap file to a negative made by printing it as a regular file.
The assertion I've heard (Mark is the last person I remember making
this assertion here) has to do with halftone separations rather than
bitmaps per se, and goes something like this: gum printers "have
found" that halftone separations give better clearer colors because
the color is laid down next to each other rather than on top of each
other. I said that might be true of opaque pigments, but certainly
not of transparent pigments, which can be printed directly on top of
each other without muddying the color.
With halftone separations, the screen angle for each of the
separations is set so the color is laid down in a rosette pattern,
each full dot being made of a rosette containing each of the three
colors, like three different-colored petals making up a flower. In
that case, the color really is laid down next to each other rather
than on top of each other, and would give you the comparison you seem
to be after. But if you were using halftone separations of this
kind, it seems like you would have said so, rather than
characterizing the negative type as a "bitmap."
So, some clarification would help me understand what it is I'm
looking at here, thanks.
On Oct 16, 2006, at 6:57 PM, Christina Z. Anderson wrote:
Good evening all,
Over the last week I have been testing four kinds of gum negs,
gum and gum over cyanotype (cyanogum). My goal was to see if
bitmapped negs produced clearer, more brilliant colors as I read
somewhere, or even worked with gum, and then to find an
acceptable, cheap, low tech beginner mode of gum printing.
I made sure to actually attach the negs side by side so all other
were exactly alike--coating, dry time, development, etc.
So here's the skinny:
1. Trigum printed with a negative on cheapy Photo Warehouse OHP
transparency with all inks, no curves
2. Trigum printed with a negative on cheapy Photo Warehouse OHP
transparency with all inks, no curves, and bitmapped 360 ppi input
3. Cyanogum printed with a negative printed on expensive
inks, no curves
4. Cyanogum printed with a negative printed on expensive
correctly for cyanotype, magenta and yellow separately, colorized neg
These are my observations (NOT declarations or assertions); YRMV:
1. Bitmapping surprised me--it actually produced a pretty darn
It was softer, a bit less contrasty, but heck, with what little ink
bitmapping uses and with the fact you can use cheapy transparency,
definitely a keeper,especially for teaching beginners low tech gum.
2. "All inks" was a bit smudgy and required drying with the PWOHP/
2400, not with Pictorico. Funny, my cyano layer printed with
spots of lighter tone--not the dreaded speckles--and when I louped
negative I saw that the printer lays down minute round spots of
color inks that in turn expose cyano differently, like little mini
Very interesting. With gum this is no problem--the spottiness, of
3. Cyanotype absolutely requires a curve--by the time the
printed in, the shadows are totally overexposed unless your image
scale to fit the 4 or 5 stops of that process's range. My next
test is to
curve just the cyano and use the two bitmap magenta and yellow
negs to print
gum over. And then next I will probably curve the individual negs
and then bitmap.
4. If not printing with a cyano underlayer, you can get an
print with no curves, neg just inverted and printed as is, and
layer with exposure, development, pigment load, brushing. But all
already knew that, I'm sure I'll be told. I prefer the all inks
to the bitmapped--I think.
5. In my eye the better print was produced by a properly curved neg,
but how will your viewer know there is a "better" rendition unless
images are side by side, you know?
6. Bitmapping didn't produce clearer, better colors because of
dots laid down side by side and not on top of one another".
7. All methods can be capable of producing fine prints, once the
gum printer can meld his/her method to whatever workflow is chosen.
8. Bitmapping has....possibilities...I'm not sure what yet, but
it really did surprise me.
If you want to see the visual, copy and paste this URL into your
and scroll down to the very bottom of the images; it'll be there.