Multilayer Printing Techniques Gum Printing techniques

Calvin Grier shows us how gum printing with multiple layers and one development works – also process which also works with Calvin’s PrintMaker’s Friend!

Writer and photography / Calvin Grier


All printmakers friends colours
All PrintMaker’s Friend’s colours

If I were to coat a sheet of paper with a thick layer of gum or PrintMaker’s Friend (PrintMaker’s Friend is a non-toxic drop-in substitute for gum and dichromate) and a high concentration of pigment and then expose it with a negative, three things are going to happen.

  • First, the print will be very high contrast, and the highlights will be blown.
  • Second, the print will be grainy because the emulsion will not harden properly and will detach in irregular patterns.
  • Third, a high concentration of pigment on the paper will leave a terrible stain resulting in a dark and muddy print.

These are common problems in gum printing and can be avoided by building up tone in layers. The traditional approach to multilayer gum printing is to coat a thin layer of gum, expose, develop, and then assess the print, adding more layers as necessary to build up tone. A slightly different approach is to coat, expose, coat, expose, etc… then develop only once. The develop-once method has multiple advantages.

  • Staining is less because the darker layers are not in contact with the paper.
  • Registration is better because the print is not submerged in water between layers.
  • It’s much faster, allowing one to make a seven-layer print in 45 minutes.

Here is a link to a video explaining the theory behind the process.

Some Gum Printing Theory Before We Begin

Whenever using continuous tone negatives, we must match the process to the density of the negative or adjust the density of the negative to the process. Failure to do so will result in muddy or blown-out highlights, as shown in the image below.

Density

It is easy to adjust the density of inkjet negatives, so we will start by creating an ideal process, and then adjusting the negative accordingly. For silver-based negatives, once the negative is made, changing the density is not always possible. In this case, we will adjust the process to match the density of the negative. Because of these differences, the workflow for inkjet and silver negatives varies slightly. Below, we are going to focus on Inkjet negatives. If you are interested in working with silver-based negatives, or imagesetter negatives, visit www.printmakersfriend.com/instructions.

Through trial and error, I have found that a negative with a density of 2.4 is the easiest to work with. To create an inkjet negative that has a density of 2.4, we need a reference such as a T3110 Stouffer transmission step wedge. It’s possible to calibrate if you don’t have a Stouffer step wedge, but I don’t recommend it. (A negative with a density of 2.4 would require about a 40-second exposure in summer sun at midday). Having a good reference will make the calibration process a lot easier.

Calibrating a Multilayer Process with Inkjet Negatives

0 Step 0: Start by making stock solutions for each layer following the recipes below.
I like to store these in rectangular sealed Tupperware containers. If you are working with gum, you will want to adjust the pigment concentrations so that, when coated one on top of the other, they give an even spacing of tone. More or less, you will double the concentration of pigment with each layer.

  Clear PMF Light Black PMF Black Water
Layer 1 33g 7g   100g
Layer 2 20g 20g   100g
Layer 3   40g   100g
Layer 4 28g   12g 100g
Layer 5 17g   23g 100g
Layer 6 + 7     40g 100g

1 STEP 1: Start by coating a small strip of paper with the layer 1 emulsion. Watch this video on coating.
Let it dry, then expose it for a random amount of time with the Stouffer step wedge. Develop in tap water for about two minutes. We want step 24 to be the first white step, which would indicate the correct exposure for a negative with a density of 2.4, as seen in the photo below.

https://youtu.be/Mz7oBYEvei4?feature=shared

Step wedge

If the tone goes all the way down to step 29, then it is too long of an exposure. Likewise, if the chart is pure white past step 11, then the exposure was too short. Use the table below to calculate the correct exposure time. In the overexposure example, the difference between step 29 and step 24 is 5. Following the table below, the exposure was 3.16 times too long. If the exposure was 100 units, we need to divide the exposure by 3.16, which means the correct exposure is about 32 units. In the underexposed example, the difference between 24 and 11 is 13 steps, so our exposure was 20 times too short. If the exposure was 1.6 units before, then we multiply by 20 to get about 31 units. In this step it doesn’t matter the starting exposure time, the calculation either way will give you the correct exposure time.

Steps Away from 24 Multiply or Divide Exposure Time by
1 1.25
2 1.58
3 2
4 2.51
5 3.16
6 4
7 5.01
8 6.31
9 8
10 10
11 12.6
12 16
13 20

2 STEP 2: Calculate the exposure times.
I created a useful tool for doing this, but for the best results, I had to fiddle with the first and last layers a little bit. Follow the table below to calculate your exposure times.

  Exposure Time or Units
Layer 1 100
Layer 2 86
Layer 3 62
Layer 4 40
Layer 5 23
Layer 6 13
Layer 7 7

If the exposure in the example above was 31 units, then multiply every value in the table above by 0.31. The first layer will be 31 units, the second 26.7, etc…

3 STEP 3: Create a digital inkjet negative that has a density of 2.4.
many systems out there for doing this. I use QuadTone RIP, but it has a steep learning curve. You can also look at Richard Boutwell’s tools and Piezography for more control. Most of these systems will have some sort of chart that has various levels of ink, like the ones shown in the photo below.

Start by printing this chart, then coat a piece of paper with the layer 1 emulsion and let it dry. Put the negative and paper face to face and expose for the time for layer 1 from step 2. Develop in tap water. Look for the amount or combination of inks that produces a good tonal scale, and a good white. In my case, with QTR and an Epson 3880 I found that 75% of the photo black ink produced a good white.

4 STEP 4: Print a step chart to linearize the process.

  • Print this step chart on your inkjet printer with the amount/choice of inks from step 3.
  • Coat some paper with the Layer 1 emulsion and let it dry.
  • Place the negative and the paper face to face and punch or tape one side.
  • Expose for the time for layer 1
  • Remove the negative, and coat the second layer. Let it dry, then expose. Coat quickly. If the first layer melts, then the print will have lots of brush strokes. I recommend doing a test between fast coating and slow coating so you can see the difference.
  • Repeat with the remaining layers
  • Develop in tap water. Developing takes about 5 minutes, and is done when no pigment is dripping off the paper. Clean water to rinse the print in is a good idea.
  • Dry

Use this tool, or any other system you are comfortable with to create a linearization curve.

5 STEP 5: Apply the curve from Step 4 to the image you want to print.
Remember to flip the image and invert it. Print with the same settings as you did for the test chart. Follow the same coating, exposing, and developing procedure as in step 4. I recommend playing around with the color of the layers. For example, adding a tiny bit of iron oxide to the first two layers, and some cyan+magenta to the fifth and sixth layers will add a nice split tone.

Printmakers friend in magenta
PrintMaker’s Friend Magenta

PrintMaker’s Friend

The multilayer technique with one development will work with gum and dichromate, but it is much easier with PrintMaker’s Friend. Here’s why:

  • PrintMaker’s Friend melts slower than gum. Gum melts very fast, so each new layer eats away at the lower layers.
  • You don’t have to worry about the dark reaction with PrintMaker’s Friend. In gum printing, as soon as the gum is mixed with dichromate, the sensitivity changes. Once it dries, the dark reaction is quite fast. Imagine putting ISO 100 film in your camera in the morning, but by mid-morning it’s ISO 200, by midday it’s ISO 800, and by the afternoon it’s totally fogged. PrintMaker’s Friend doesn’t have this problem. You can coat one day, come back a week later, and continue where you left off.
  • After making a gum print, you must clear out the yellow dichromate stain in the paper. PMF doesn’t leave a sensitizer stain, so there’s no clearing step.
  • The best part of working with PrintMaker’s Friend is, it is certified non-toxic by the Arts and Creative Materials Institute.

Calvin Grier is a wizard of the carbon transfer process, and dabbles with gum printing. Over the last seven years he has taught over 120 students from 38 different countries. Besides printing, Calvin is an avid rock climber, musician, and father to a three year-old little girl. Read a portrait of Calvin Grier.

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