VDB and hu-mi-di-ty
As ive read with ziatype and Pt/Pd humidity plays a big role in the contrast of the final print. Im curious if the same is true for van dykes. Mine have been coming out rather flat and while its mostly the negs im wondering if steaming the paper could help.
Printing on arches platine, double coating, and ive recently bought some potasium dichromate though ive not used it yet.
Would steaming make a difference?
The RH in my dark room can range from 35% to as high as 65-70%. Normally will coat when it is 45-65%, if that helps. Below 45% I will humdiify the room and set the paper out in the room to reach the same RH as the room prior to coating.
Before looking at the RH, perhaps coating some paper like you would normally do for a negative, but use a step-wedge to check your processing. If the step wedge comes out the way you want, contrast wise, then it may be your negatives just need a contrast boost. There are others here that should have a better idea, this is just how I would approach.
I have found that humidity is more important for a paper like Platine than others (ie Stonehenge). I was getting very poor dmax with low humidity (around 35%) with Platine. Using a vaporizer in the coating area made a huge difference. I try to climatize the paper at around 60% RH for at least an hour before coating, during coating and as as the paper is drying. I believe that Sandy King recommends 60% RH for all iron processes.
From everything I've read on VDB printing, Potasium dichromate doesn't work for controlling contrast. Your basically stuck with the contrast of your neg.
Late to this thread, but IME humidity is important for Van Dykes. I print them in my kitchen, and generally put a pot of water on the stove to boil very, very gently during the coating / drying / printing process. I seem to get better D-max and smoother tones this way.
I've never found dichromate useful. It is a silver bleach so it will remove highlight fog but it also works on the shadows and lowers dmax. I suppose one could calibrate the dichromate control, but IME, it seems better/easier/more useful to get the correct contrast in the negative.
Originally Posted by davido
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You can use a quick dip in very very dilute rapid fix as a van dyke bleach too. It's milder than dichromate, so it can be useful for clearing highlights.
-- Ole Tjugen, Luddite Elitist
Dichromate is useless for controlling contrast with VDB. It is a real pity that this error has been repeated so many times in the literature, even in the first edition of Christopher James' otherwise wonderful book on alternative printing.
Originally Posted by smieglitz
What dichromate does is reduce priting speed, and some people mistakenly concluded that this resulted in a change of contrast. Not so, and if you doubt it run some tests yourself with a step wedge.
As for humidity, it is as important in VDB as it is in kallitype and Pt./Pd. printing. A change of RH of 10%, from 50% to 60%, can almost double the printing speed of VDB. Higher RH also gives much greater Dmax than low RH. Again, check this yourself with a step wedge.
Sandy, since Kallitype process has some similiarity to VDB, does your rejection of Dichromate as useless also apply to Kallitypes? My presumption is that slowing down the printing process means that the high value areas don't fully develop; therefore they remain whiter.
Originally Posted by doughowk
No, my comments apply only to VDB, or any similar process that uses ferric ammonium citrate as a sensitizer.
True kallitype uses ferric oxalate as its sensitizer, and dichromate is very effective as a contrast control, as it is with platinum and palladium printing.
Dichromate may reduce printing speed slightly with true kallitype, but it is accompanied by a real change in contrast.