I have way too many suggestions and don't even know where to start without writing a tome. And I guarantee you that my suggestions will bring a host of people responding with "not in my practice!" which makes it even harder for you to figure out your own truth. So here are some ideas for you:
Use a Stouffers and determine a standard printing time--here in Mt 6 min UV is perfect for most colors with a 15% am di mixed 1:1 with gum/pigment to am di, but even as low as 3 minutes or as long as 12 may work for you and still give white at the high end. You want to look at a step wedge that clears to paper base white with not a lot of steps of block up at the first few steps. I know that sounds strange to someone like yourself who knows photo, but gum is not like BW--you are just hardening a layer of DEPTH of gunk. And everything I say may be completely different in FL vs. MT--I have 20% humidity right now! You may need to expose less. Yellow takes more time, thalo, and magenta less. Black a lot. These are all things you'll find out with a step wedge, but a good starting point might be something like 12-15 minutes to get a bunch of the steps on the wedge to merge and then work back from that time.
If you are going to size, size your step wedge paper, too. If not, don't size the paper for the step wedge.
Take good notes and in the beginning standardize so you can get a handle on the process.
The difference with gum and PDN vs. other processes and PDN is that with gum you almost have to choose an acceptable standard printing time and run with it instead of finding a "perfect" printing time. It's just a bit different than, say pt/pd. It is not a one-shot deal, because development can take care of variables and humidity introduces variables as does thickness of layer, depth of pigment, blah blah blah. Sometimes a perfect time according to a step wedge with only Step 1 at maximum black is simply not enough time to harden a sturdy layer to withstand a good development.
You may notice, when doing PDN and choosing the color that gives paper white, that yellow responds differently than blue and magenta and others. Yellow also produces a different curve. All three are reverse contrast curves but yellow is shaped differently. It stands to reason because yellow and dichromate are the same filtering color. In fact, yellow and dichromate with no pigment are similar in curve shape and both different than blue and magenta. All of this depends on your printer, though, very much so. I know Don Bryant and I rarely come up with the same colors for things.
I would recommend starting with an image made from a negative with no curve and just printed out all inks. Print it in black pigment. Then do PDN, get your curve and color figured out, redo the same print a la PDN and see the difference. I make all students do that now, because a side by side will indicate the benefits of curves and gum.
You can also download my article on how I gum print here:
and also a bunch of teaching pix are at CZAphotography.com and then click on Learning and then on Gum Dichromate.
Sorry this is so disorganized but it's easier to address individual questions than the whole shebang.
----- Original Message ----- From: "Weber, Scott B" <firstname.lastname@example.org>
Sent: Tuesday, January 22, 2008 4:03 PM
I want to start gum printing with PDN, any suggestions? Does any one have curves or advise about curves to share?