Tag: gum printing

Ammonium vs Potassium Dichromate

May 25, 2013

rabiephotography asked: Hey thank you so much for sharing your knowledge and amazing art ( your results are brilliant!) I am keen to give it a try and was wondering if you can talk about the sensitizing process as I need to order the chemistry; not sure whether to use ammonium dichromate or potassium dichromate ? (and what’s the difference in terms of use). Thank you!

Thanks. I’ve been using Ammonium Dichromate for my sensitizer for over ten years. Christopher James prefers the Potassium Dichromate and says it gives less contrast than the Ammonium Dichromate. I once tried (unsuccessfully) using Potassium Dichromate a couple of years ago, but since all of my research and results are based on using Ammonium Dichromate, I’d decided to stick with what I know. Photographer’s Formulary also requires additional paperwork to be submitted when ordering Potassium Dichromate. Hope this helps. 
Tony

Color management

April 22, 2013

senojev-deactivated20171203 asked: Great work to which I aspire! Thanks for sharing all of your experience with the masses who struggle to achieve your results. I have almost finished reading your Journal and have a question on the March 27, Color Management note. You say that you increase the cyan hue by 30-45 and saturation by around 30. In an earlier note, you note that you used Color Balance. Am I correct in adjusting the cyan in Hue and Saturation? My Color Balance adjusts hue in shadow, mid & HLights.

I first adjust the Cyan: >Image>Adjustments>Color Balance.  I slide the arrow towards the Cyan aprox. -35 or so (it will appear as -35 in the left Color Levels window) keeping he “Tone Balance” at “Midtones”.  I then adjust the Hue/Saturation: >Image>Adjustments>Hue/Saturation.  I slide the Saturation arrow +30 or so.  Finally I Multichannel: Image>Mode>Multichannel.  Hope this helps.  Tony

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.