Tag: Negative

Precautions with Potassium Dichromate

February 8, 2013

neiromobile-blog asked: Hi, Tony! I really want to try gum bichromate printing, but I am very concerned about the toxicity of the main component — potassium dichromate. I do not have a separate room for the process at the moment. Can I do this at home? In the bathroom. What safety precautions when working with potassium dichromate?

There is a long tradition of bathroom darkrooms.  When I first started with Gum over ten years ago, I used the tub in my bathroom for about a year or so making prints using 13×19 inch negatives in 16×20 inch trays.  It wasn’t ideal but it worked-a lot of my preliminary research was done during that time.  It’s important to have a healthy respect for the Dichromate (I use the Ammonium Dichromate).  Wear a mask when dealing with the dry chemistry and wear gloves when handling the Dichromate (wet or dry).  Fastidiousness is a necessity–make sure to clean all areas in contact with the sensitizer.  Refer to the MSDS sheets for further handling precautions.       Tony

Pigments

January 29, 2013

shouldhaveswipedleft-blog asked: Dear Tony, I’m just starting out with this process and want to begin with single color (black or sepia colored) prints before moving on to full CMYK. Do you have a preference in pigment for single color prints? Thanks!

I haven’t done much single color printing but have always had good results with the Schmincke brand of watercolors.  You may try the Burnt Sienna for a sepia.

Looking for step #3 in the third set

November 12, 2012

davidh47-blog asked: Hello Tony,I really like your work and your openness. Thank you. In part 2 of printing the negative you say that you expose and develop until you see a slight density in step 8. However in part 3 you expose and develop for slight density in step 3. How do you measure this if you have previously fully exposed that step (or am I being stupid :?) ) . Once again, thank you for sharing. David

Excellent question.  While the print is developing and still wet, I hang the print from one corner and inspect the step tablet.  In areas of exposed gum, the print is glossy and where the print releases the gum the print has a more matte surface (usually within about 30 second–be careful not to let the print dry too much until you’re ready to finish developing).  I look at the print from an angle where I can see the light reflected.  Hope this helps.  Tony

Stouffer to curves

August 13, 2012

ivantheboneless-blog asked: Is this what I would do with my own printer? Print out 100 values of gray, decide what values match the stouffer scale and then create my own curve that I would apply to the negatives? Now where I get really confused is how does it correspond to my negatives. I am assuming that it takes the values of the original negative and compresses them into 8 values. What if you have a high key image vs. a low key image? Does that matter? I don’t even know if I am asking the right questions!!! Thanks!

Correction to answer I just published.  21% of black ink is the equivialent to step #2 on the step guide, 49% is the equivalent to step #3 and so on.

Yes, once you find the black ink squares that are equivalent to the Stouffer steps–those percentages of black ink become your “out put” in curves.  The “in puts” are the numbers from 0-100% in curves divided into aproximately 8 equal points (0, 16, 30 and so on).  Defining the D-max and D-min will depend on your printing method.  For my gum prints, I can’t print higher than 85% of black ink on the shoulder and there isn’t much of a printable difference below 21% of black ink in the toe.  Once you find a curve that works for you, it can be applied to any image regardless of contrast.  Hope this helps.

Stouffer step equivalents

August 13, 2012

ivantheboneless-blog asked: Hi Tony – I have an involved question and it might be more time then you have to answer, but I will ask it anyways. If it’s too much to answer – no worries. I am so confused about the curves. Did you make 100 squares of percentages from black to white, print it out on your inkjet printer and then visually equated the values to your stouffer scale? So that step #2 on the stouffer scale equals the 16th value of gray on your inkjet scale?

I did make squares of percentages, but 50 squares (at 2% intervals) instead of 100.  I then printed it out on the Pictorico, OHP Transparency film using my Epson 1400 printer with the Clarion Inks.  I used a Densitometer to measure each square to get a numerical value of the percentage of black ink that was equivalent to the numerical value measure from the the Stouffer step guide using the Densitometer.  So, yes 16% of black ink is equivalent to step #2 on the Stouffer step guide.  Before I had the Densitometer, I just “eyeballed” it by using a couple of index cards with a hole punched in each to isolate and compare the different ink squares with the Stouffer steps to try and find the match by eye.  Not ideal but it puts you in the ballpark.

Preshrinking paper

June 25, 2012

bufetslow-blog asked: hiI am very surprised by your gum bichromate photography and wanted to know what a paper you use and how to build Preshrinking paper

Thank.  The paper I use is the 250 gram Rives BFK.  For preshrinking: I boil water enough to fill a tray a place the paper in the hot water one sheet at a time.  After 10-15 minutes I flip the stack of paper over and remove each sheet individually (first in first out) and hang by clothespins on two corners. You can check out my February 07, 2012 post “Sizing the Paper” for detailed description on my sizing paper process.

Step tablets

April 23, 2012

pleasekillmenowforiamworthless asked: Hi, I am a student at Utah State and I am hoping you can give me a few tips. I have been looking at your workflow for negatives and I am wondering where you got the files for your registration marks and the step tablets? I have been having a hard time with registration and I am looking for a better method. Second, I am using a NUARC machine for exposure, do you have any experience with those units? I am trying to nail down a good exposure time for each layer.

I found the registration marks I use online years ago and I make my own step tablets in Photoshops by combining layers of rectangles filled with different percentages of black ink to correspond to the outputs of my curve.  If you send me an email agonzale@qc1.qc.edu  I can send you TIFF files of the registration marks and step tablets.  I haven’t used a NUARC machine for exposure for gum printing.  However, I tell my students to test and base their exposure times on the steps on the step tablet since everyone’s exposure unit and development method is different.

Workshops

April 23, 2012

akewaldronart asked: Hey man. Your work is incredible. I’m just about to start trying some alt. pro. stuff and you are definitely going to be an inspiration. If you ever do any workshops or anything I’d love to check one out. – Jake

Thanks a lot.  I don’t have any workshops scheduled, but I will definitely announce any that come up. – Tony