The Gum Printing Papers – synthetic sizing

Peter J. Blackburn begins a two-part informal “white paper” discussing synthetic sizing while reviewing two papers that use sizing and one that doesn’t!

Writer and photography / Peter J. Blackburn


Once again, the time has come to write about some wonderful watercolor papers currently available, which I find to work quite well for gum and casein bichromate printing. Those who have read my introductory gum printing articles know that applying supplemental sizing, such as formalin, glutaraldehyde, and glyoxal, has never been a part of my workflow. Instead, I have relied upon papers incorporating nontoxic, inert, synthetic sizing materials, such as alkyl ketene dimer (AKD). The two papers reviewed here meet that specification. And there are others readily found under the well-known brand names of Fabriano (Artistic0) and Strathmore (500 Series).

As of this writing, my preferred paper for professional work is Canson Heritage (CH). It can be found in the usual range of surface textures (HP, CP, and rough), two weights, and four formats. Both rugged and elegant, the internal and external sizing of CH is amazing. It provides a delightful surface for my pigments to take hold and shine, even after the usual presoak. My whites (highlights) print clean and crisp. It’s the best gum printing paper I have ever used up to this point.

My choice for experimental work, test prints, and practicing is Richeson Bulk Watercolor Paper (RBWP). Nicely sized and nicely priced, those starting out in gum printing might consider this offering from Richeson. Again, I have not found the need to add any additional sizing to this paper. However, keep in mind that this paper contains no cotton.

Here you can examine a few samples of both, which are explained in the descriptions.

Canson Heritage

Two Prints in Process, 2023  This pair of gum prints (still in process) have already received three layers of color with more to come. No added sizing. I am using only a 3% potassium dichromate solution. Colors include PY151, PO62, PG18, PV19, PR254, PB29 and PBr7. Notice the clean whites.
Two Prints in Process, 2023  This pair of gum prints (still in process) have already received three layers of color with more to come. No added sizing. I am using only a 3% potassium dichromate solution. Colors include PY151, PO62, PG18, PV19, PR254, PB29 and PBr7. Notice the clean whites.
Anne's Floral in Time, 2023  Here is a standard tricolor print. Canson Heritage does an excellent job working with your pigments and negatives to render what you intend. Please note that all of the images in this essay are printed from laserjet negatives printed on economy 20-lb paper.
Anne’s Floral in Time, 2023  Here is a standard tricolor print. Canson Heritage does an excellent job working with your pigments and negatives to render what you intend. Please note that all of the images in this essay are printed from laserjet negatives printed on economy 20-lb paper.

Richeson Bulk Watercolor Paper

Rising Red Roses, 2023   Richeson Bulk Watercolor Paper is an economical choice for gum printing right out of the package! Again, no supplemental sizing is needed for colorful, expressive images.
Rising Red Roses, 2023   Richeson Bulk Watercolor Paper is an economical choice for gum printing right out of the package! Again, no supplemental sizing is needed for colorful, expressive images.
Flowers in Blue Pot, 2023  Here is another tricolor print on RBWP. While the sizing is not quite as robust as the Canson choice, this paper allows colors to mingle in appealing ways. I enjoy the feel of many of the images produced on this paper. And, if my negatives print well on Richeson, they'll rock 'n' roll on Canson!
Flowers in Blue Pot, 2023  Here is another tricolor print on RBWP. While the sizing is not quite as robust as the Canson choice, this paper allows colors to mingle in appealing ways. I enjoy the feel of many of the images produced on this paper. And, if my negatives print well on Richeson, they’ll rock ‘n’ roll on Canson!
Memorial, 2022  My final RBWP sample to display. Again, my emphasis here is that no supplemental sizing is ever applied to my papers. And only a small amount of dichromate (3%) produces the exposure.
Memorial, 2022  My final RBWP sample to display. Again, my emphasis here is that no supplemental sizing is ever applied to my papers. And only a small amount of dichromate (3%) produces the exposure.

And Now for the Hat Trick. It’s a Zinger!

This essay is really an introduction to my next one, scheduled for publication in a few months. We’ll take a deeper look at sizing and other printing aspects that affect the final outcome. And in preparation, as a teaser, if you wish, I leave you with one last tricolor image (see far below) to examine.

However, it was not printed on synthetically sized paper.

In fact, this was printed on paper that many gum experts claim must first be treated with supplemental hard sizing. And what size is that? You guessed it: formalin, glutaraldehyde, or glyoxal.

But none was added to this paper. Zero.

Indeed, no sizing of any kind was added to this paper. None whatsoever.

The paper was only presoaked for shrinkage control before printing.

My only hint as to its’ identity is that this fine art paper is one of the most beloved in the world.

It’s also one of the most shunned for gum printing.

Can you guess the paper?

You might be interested in knowing this, too. All three layers with drying cycles and a clearing bath in potassium metabisulfite were completed for the print below in well under three hours. And with perfect registration.

See for Yourself.

Beginning August 6 through September 22, almost two dozen tricolor prints produced on this “unsized” taboo mystery paper will be on exhibit. Come to the Goodrich Gallery, located in the Arts District of Dallas, Texas. 

No worries if you can’t make it. Several exhibition images will be reproduced for the next article. We’ll discuss them, along with gently exploring a potentially sticky wicket in gum printing. And I’ll reveal the identity of the mystery paper, too. See you then!

Festive Floral, 2023  This 22″x 22″ image is a mixed media piece: tricolor gum bichromate print, gouache, and mulberry paper. No size was added. Can you guess the paper?
Festive Floral, 2023  This 22″x 22″ image is a mixed media piece: tricolor gum bichromate print, gouache, and mulberry paper. No size was added. Can you guess the paper?

Peter J. Blackburn, MA, is an artist who has been working in gum and casein bichromate printing for over thirty years. He is represented by Afterimage Gallery, Dallas, Texas. You can also see Peter J. Blackburn’s gallery or read more articles he has written. Peter also conducts occasional workshops and is available for small group or one-on-one instruction. Learn more.

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