In my last post, I mentioned briefly a couple of characteristics of printing ink. I thought I would take a little bit and elaborate on them, as well as on a couple of the materials that can be used to adjust those characteristics.
I should mention here that I basically use two types of ink in my studio: Etching ink (primarily black, but also a couple of specialty colors such as graphite) and lithographic ink. These are all oil based inks, which means that they have as their primary vehicle one burnt plate oil in one or more if it’s grades. The characteristics I am going to talk about here are not specific to any one particular type of ink, but each ink (be it oil based, oil miscible, acrylic, whatever) will exhibit some combination of these which may make it more or less suitable for a particular task.
There are three basic working characteristics of ink that are of interest. They are:
Viscosity (sometimes referred to as stiffness) is the resistence of the ink to flow. Does it stand up on the slab (see the photo at the head of this post) or does it flow out into a puddle. Inks made with burnt plate oil are to some degree thixotrophic, which means that as the are worked, they become less viscous. This is also true as they are warmed. Inks that are overly stiff may not roll out properly or may be difficult to roll to an appropriately thin layer, resulting in over inking.
Tack is how sticky the ink is. Specifically, how well it sticks to another surface (the ink slab, the roller, the plate, the paper). If the tack is too high, you can actually pull the surface off the paper rather than transfer the ink to it. Not good. Not enough tack and the roller has a hard time picking it up and transferring it.
Length is the hardest characteristic to grasp. Perhaps it is easiest done by analogy. If melted cheese were ink, parmesan would be a short cheese, mozzarella would be a long cheese. You test length by pressing your ink knife down flat in the pile of ink and then lifting it straight up. A short ink breaks almost immediately. A long ink pulls up long strings, like eating a hot slice of pizza. You generally want to work with a shorter ink for lithography. If your ink is too long, you can bridge fine detail.
These characteristics are independent, but as you move one, you will tend to move another. If you lower viscosity, you will tend to lengthen the ink as well. If you increase the tack, you will probably also increase the viscosity.
Ink as it comes from the can varies a good deal as the size and shape of the pigment particles have a significant impact on the handling characteristics of the ink. Consequently as you mix color, the character of the ink changes as well and some adjustments to the workability are often required.
There are a wide array of modifiers available. They may be used singly or in combination as required, but should always be used carefully to avoid damaging the fundamental character of the ink.
- Burnt Plate Oil – in its light grades (#00, #3) it will lower viscosity, tack and increase length. The higher numbers (#5, #8) will do the opposite, increase viscosity, and tack with less affect on length.
- Easy Wipe – primarily reduces tack, making wiping an etching plates easier.
- Magnesium Carbonate (“Mag”) – increases viscosity and reduces tack and length
- Setswell – reduces viscosity, tack and length