One essential in every calligrapher's tool kit is gum arabic. What the heck is it and why do we need it? Here we go...
Gum arabic, also known as acacia gum, is a natural gum made from the hardened sap of the acacia tree. It is used primarily in the food industry as a stabilizer (helps to preserve a foods structure), and it is edible. It is also used in printing, paint production, glue, cosmetics, ceramics, and the list goes on. Yeah for Mother Nature!
As calligraphers, we use gum arabic as a binder, to control viscosity, to add a bit of luminosity, reduce feathering and bleeding, and to prevent cracking of ink. Let's touch on each of these...
Binder - We add gum arabic to a mixture of gouache and water to make sure that the resulting ink sticks to the paper. As the water evaporates, the gum arabic binds the gouache to the paper. Gouache already has gum arabic in it, but I like to add more to ensure that the ink is not going to wipe away (especially if you need to erase any guidelines). To make ink from Pearl Ex Metallic Pigments and water, you must add gum arabic, it is the only component that binds the pigments to the paper. Without it, the pigments would wipe away after the water has evaporated (when the ink is dry).
Viscosity Control/Luminosity/Anti Feathering - We can add gum arabic to an ink to increase its viscosity, or "thicken" it. I have added gum arabic to certain fountain pen inks to be able to use them with a nib. The addition of gum arabic can also prevent that fountain pen ink from bleeding (not always, paper is another variable). We all love the way wet gouache looks, it glistens, its luminous, and it stands on top of the paper...and then it dries, and depending on the color, can look a bit chalky or dull. You can add a few drops of gum arabic to reduce a bit of the chalkiness and increase luminosity.
Cracking Ink - I'm talking specifically about Bleed Proof White here...it can crack when dry, and if you have ever received an envelope addressed with BPW and its all cracked and smeared, you know how horrifying this can look. I add just a drop or two of gum arabic to BPW to help prevent cracking, chipping (again its a binder), and to make is just a tad less chalky looking.
Liquid vs. Powder Gum Arabic
Gum arabic can be purchased in two forms, liquid in a bottle, or solid...in the form of crystals or powder. Gum arabic crystals are dissolved in water and added to paints, etc. Powder gum arabic is just crystals ground very finely. I will focus on how we use liquid vs. powder for our inks.
Liquid Gum Arabic - you can find liquid gum arabic at your local art store, craft store, and online retailers. There are several brands, including Daler-Rowney, Holbein, Schmincke, and Winsor & Newton. I use Winsor & Newton because it is the brand I usually see in my local shops. I use liquid gum arabic when mixing up gouache for ink, anywhere from a few drops to 1/8 teaspoon, depending upon the quantity of gouache I am mixing. If I need to add water to my Pearl Ex ink, I will also add a few drops of liquid gum arabic, just to make sure there is enough binder in it.
Powder Gum Arabic - I do not purchase crystals, I use the powder in a jar from Jacquard, and is available at both John Neal Bookseller and Paper and Ink Arts. I use powder gum arabic when first mixing Pearl Ex pigment. I use four parts Pearl Ex, 1 part gum arabic, stir to combine, then add the water. I approach ink mixing like baking, mix like with like...liquids with liquids and dry with dry. I do not want to add powder gum arabic on its own directly to water as it might cause clumps, and clumpy ink is no bueno. If you only have liquid gum arabic, it works with Pearl Ex pigments just fine. I would add liquid after combining the pigments and water - so cut back a bit on the amount of water, add liquid gum arabic, stir, and then add more water if you want the resulting ink thinner.
How much Gum Arabic is enough?
The only way to truly know is to test your ink. You must wait until your ink is completely dry first. Then see if it will wipe away or smear with your finger. Try an eraser on it, does it stand up to erasing? If the ink smears in any way, you don't have enough gum arabic in your mix. If I need to add more gum arabic to ink that is already mixed, I always add liquid gum arabic, and then will test again. If your ink has "collapsed" in the center, it is not due to gum arabic (too much or not enough) it is because your ink is too thick, and when it is drying (from the outer edges to the center), the dry portion cannot support the wet center (it is heavier because water is still present), and so it collapses. Thin your ink to prevent this.
Do I need to add Gum Arabic to Acrylic Ink?
No, any acrylic based ink does not require the addition of gum arabic. Acrylic ink/paint is a whole different animal, composed of pigment particles dispersed in an acrylic polymer emulsion. Once the water in the emulsion evaporates and/or is absorbed by the paper (or any support), a film is created, trapping the pigment particles. If you need to thicken an acrylic ink, use an acrylic liquid thickener.
Do I need both liquid and powder Gum Arabic?
Nope, if I could only purchase one, it would be the liquid version, it would be more versatile. But I have and use both. I use the liquid with gouache, and the powder with Pearl Ex. Liquid gum arabic will darken over time, so if you are doing any archival work, it is suggested that you use the powder version. Liquid gum arabic can also go "bad", as the more you use it and expose it to air, contaminants get into the bottle. To mitigate this, I transfer small amounts into a dropper bottle. Powder gum arabic will likely have a longer shelf life.
As you all know, liquid gum arabic is sticky and gooey, and eventually that twist off top will get very hard to twist off, so wipe off the top of the bottle each time you use it.
Hopefully this answers all of your questions and them some. I know gum arabic can be a "sticky" topic (thanks David for the pun), if you have anything else you would like to know, please feel free to shoot me an email and I will be happy to respond.
So that is the 411 on Gum Arabic...happy ink mixing!