On Apr 26, 2006, at 2:56 PM, Marek Matusz wrote:
> Katharine,
> It is always good to look at actual prints, though imperfect they
> might be. Thanks for posting your work. I think that you can easily
> see a big difference of back vs. front exposure.
Of course, I can see a big difference between back vs front
exposure on the plastic, just as I saw and reported with the earlier
comparison I showed using ivory black, but the point here was that so
far I haven't seen anything in my own experiments that looks better
than I could do with a one-coat (front-exposed) on paper. I was
looking for more tonal delicacy, as Peter put it earlier.
> Although the recipes and practice might be far from perfect it is
> this first observation that leads to a new discovery.
Yes, I agree, and I think that's what happened before: my initial
experiment led to your more interesting results.
> To clarify my recipe, my gum mix consisted of 0.25 g of dry lamp
> black from Daniel Smith (or is it called carnbon black?, can't
> remember at this moment),
Obviously there's no way to compare this to the amount of paint I'm
using, as we don't know how much pigment is in a given amount of a
given brand of a paint made of a given pigment.
> 3 grams of dry gum (I actually used 10cc of 14 baume gum which is
> about 30%)
By the same (or a similar) token I can't tell how much actual gum was
in the emulsion, because I start with an amount of pigment-gum mix
rather than with a given amount of premixed gum, to which a given
amount of pigment is added. I know that the pigment-gum mix stock
solution I'm using was made from 15 ml premixed gum and 5 grams of
paint, and I know that I'm using 2.5 ml of that mix. But another
wrinkle is that the paint contains gum arabic as well, and there's no
way of knowing how much.
> and 0.6 grams of ammonium dichromate (2 cc of 30% solution), all in
> 12 cc of solution.
I used .135 g dichromate (.5 ml of 27% solution) in 3 cc total
emulsion. For the first one (#3) I used .675 g dichromate (2.5 ml of
27% solution) in 5 cc total emulsion.
> The total volume of the solution is incidental as it only serves to
> dissolve everything and make the solution spreadable. Once the gum
> dries, it is the weight of dry components that will determine final
> properties of the mixture.
Seems plausible in theory, but given my own observations over time I
wonder if this is so. I might have to drop my cleaning and sorting
and try mixing a different dichromate solution to see if less
dichromate in the same amount of water has the same effect. If so,
then I'd have to agree that the reduced DMax in #3 is caused by
something other than more water in the emulsion.
It seems like anyone who wants to investigate this effect seriously
should do as Marek is doing; use powdered pigment. I'm not sure my
initial results have excited me enough to get that serious about it,
but maybe after I get moved and set up again. But one thing this has
definitely taught me, is that if one is going to print on plastic,
one should definitely print from the back.
Katharine
Received on Thu Apr 27 10:15:04 2006
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