All About Paper, Part II - Sizing

 All About Paper -- Part II – Sizing

Sizing is an additive to watercolor paper to make it a more durable surface for painting. It reduces absorbency and adds stiffness to paper. Without sizing, it would be like painting on a paper towel – the moisture would soak in and spread throughout the paper. Sizing can be added to the pulp vat for internal sizing, or it can be applied to the surface of the paper, or both – some papers have sizing added to the surface and also internally. There are two common products that are used for sizing, and there are pros and cons to each of them. 

The Collection, Watercolor Paper by Hahnemuehle

Vegetable sizing is STARCH, and animal sizing is GELATIN. Think of a vegetable starch, like a cornstarch -- it can be easily and quickly dissolved in cold water. Gelatin, on the other hand, is much harder to dissolve and requires boiling water and a lot of effort. That's why it is also used as a glue and as a surface preparation for oil painting (in it's form of rabbit skin glue), as well. 

Annie Strack pulling handmade watercolor paper in Fabriano, Italy

When dried, the starch products are easily reconstituted but the gelatin products require much more effort to reverse or dissolve. So, as a paper sizing, vegetable sizing will not hold up to a lot of "abuse" -- scrubbing, multiple layers, lifting, masking, over-working, etc., whereas traditional gelatin sizing is much more durable. 

testing different mediums on a paper

Vegetable sizing is much brighter, whiter and doesn't discolor, while gelatin sizing often causes a warmer tint. Gelatin is a byproduct of meat production (animal hides, usually bovine) so vegans and some religious doctrines avoid it. These are the pros and cons to consider for each, and it’s up to the individual artist to decide which is best for them. 

Read the other articles in this series: 

All About Paper - Part I - Surface Textures 

All About Paper - Part III - Weight 

All About Paper - Part IV - Handling

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Annie Strack is an industry trained expert in the uses and properties of artist materials. She is a Brand Ambassador for Hahnemuehle Paper and several other companies, and teaches at art centers, art supply stores, and workshops around the world.