Paper and fabric that you can find in art supply stores come in two types: sized and unsized (raw).
Sizing is applied to prevent color blotting or ink bleeding when painting on substrates such as Japanese washi paper, silk canvas, and wood. Sizing refers to the coating process and we call “size” for the liquid used for sizing. In Japan, animal glue-based sizing liquid is commonly used which is called “Dosa (礬水), ” and the sizing technique is also known as Dosa-biki. Dosa is not something that can be manufactured in a certain way and achieve the same effect on all substrates.
Animal glue is made by boiling and refining animal bones and skins which is the reason why they can change their form to preserve the condition and its individual differences thanks to the nature of the materials, therefore, Dosa liquid also requires certain knowledge and understanding of the materials to use it.
Nowadays, although you can find some sized paper in stores, there are still many types of raw paper, and materials like silk, linen and wooden boards mostly require artists to size the substrate themselves. Moreover, for some mounting techniques such as Hyouso framing or Urauchi backing, it is necessary to have artwork on sized washi paper or silk canvas. For example, during the process of Urauchi backing, water is sprayed on the artwork, so color can be spread out from the piece depending on how well it has been coated with sizing liquid.
There is an advantage of doing the whole sizing process by yourself from making sizing liquid to applying even if it’s very time-consuming. It not only increases the choice of base material, but also has the potential to expand the range of gradation and blending of sizing liquid according to color materials, substrates, and painting techniques.
However, due to the nature of substrates (like washi paper and silk) with animal glue, which is susceptible to high temperature and humidity, Dosa liquid may not work well depending on the environment and the compatibility with Dosa liquid. It is possible to control this by adjusting the concentration of the sizing solution and the number of times it is applied, but this requires not only knowledge and experience with substrates and color materials but also researching and collecting data.
At PIGMENT TOKYO, we have created samples by comparing the differences in Dosa concentration on various substrates, so let me introduce some of them here!
In this article, PIGMENT TOKYO's original animal glue is used for the experiment.
When making Dosa, alum is generally added to enhance the effect of hardening the film of animal glue, but if the glue already has high jelly strength, the film will harden without using alum.
We recommend approximately 3-4% concentration for washi paper and 1.5-2% for silk canvas when making Dosa with our animal glue, however, as I mentioned above, the sizing effect varies depending on the temperature, humidity, and substrate, so it is important to adjust the concentration and the layers of application according to your environment and your preference.
There are two types of animal glue we recommend using as Dosa liquid: a sheet type “Pig Skin Glue” and “Pig Glue for Sizing 20％” which is a 20% concentration of the sheet type glue.
Although sheet-type animal glue takes time to make dosas, it can be stored at room temperature for a long period. It’s convenient and is recommended if you plan to make a lot of Dosa. Mold may occur under high temperatures and humidity, so please store it with a desiccant.
“Pig Glue for Sizing 20％” only needs to be diluted with water before use, therefore, it is a perfect product if you just want to experiment with it for the first time or only need a small amount.
It contains preservatives and can be stored in the refrigerator for about one year.
The product will solidify at low temperatures, so please boil the bottle in hot water or transfer an appropriate amount to another container and warm it up before use.
Please refer to the article below for details of the product and about the Dosa solution made from sheet-type animal glue.