Sizing is a highly important and integral element when creating paper, we thought it was so important that it deserved it’s own blog. We quickly covered what sizing is in our Basic Breakdown Blog of Paper as sizing is something that happens in the paper making process and we suggest you give that blog a read as we think it’s full of useful information. However, we wanted to go into further detail so you can see why sizing paper is an important step and why you should make sure whether a product is sized or not; in it’s most simplest term, a size is used so the paper becomes less-absorbent which is really important with something like watercolour because so much water is needed.
Two of the main ingredients in paper are fibres and water. These fibres usually come as cotton or cellulose depending on the quality. Fibres generally love water which is perfect when you are in the process of creating the paper as it can soak up the water in the vat of the machine to make the paper pulp mixture. However, if a size isn’t added during this process it means the fibres love of water is still within the paper once it is shaped and dried.
The unsized paper, also known as ‘waterleaf’, now has the ability to absorb fluids readily and instantly like it did before it was paper. Fluids will be able to spread randomly and bleed through on the sheet. It’s love of water may not be a desired element when creating art, this type of absorption is something you can’t exactly control and as an artist - depending on what you want to achieve - you may want to control this.
You can still purchase paper that is unsized such as blotting paper, paper towels and tissues as well as some artist paper. However if you want to use something that needs water like watercolour or something that is known for bleeding such as Promarkers, we suggest purchasing appropriate paper that is specifically made for that medium.
Ink on sized Khadi Paper
A paper is sized so it becomes more water-resistant and less absorbent, this will also highly reduce or eliminate bleeding as it coats the cellulose fibres. Additionally it also protects the sheets from breakdown due to oxidation and slows down its ageing. Sizing can also add adhesive qualities and strengthens the sheet, so it really is an important step when making paper.
There are two sizing methods you could use; you can add the sizing agent either internally or externally as well as using both sizing methods on one singular sheet which is something high quality paper does;
Internal Sizing is combined whilst the paper is still a mixture of water and fibre. The Beater (also known as a refiner or a vat if you are making paper by hand) is the mechanical device for paper pulp and is considered the most crucial part to the paper making process as various other ingredients can be added during this time along with the pulp fibres such as fillers and dyes. It is an oval-shaped tank that includes bars and a rotating beater roll. The pulp slurry mixture of water and fibre rotates between the bars resulting in the formation of paper, whilst it is this mixture, the other ingredients are added before moving on to the next stage.
You can include a minimal amount of internal sizing, this process is called slack-sizing which means it is only slightly water resistant. Adding a larger amount of size means it can withstand plenty of water and can be used for offset printing; this is called hard-sized.
External Sizing is applied after the paper has been formed. Also known as surface sizing, this process can be more time consuming. However unlike internal sizing it adds a protective coating to the sheet itself. External sizing is something you can easily do at home compared to internal sizing (unless you are making your own paper). There are three sizing methods and for each method the sheet has to be completely dry before adding the size. The three methods are;
Brushing - Using a brush, you paint on the size and can add multiple coats if you wish.
Spraying - To begin you combine the size with water and then spray onto the paper.
Tub Sizing - You soak the sheets in a tub of size which is then pressed.
The Paper-Making Process
The solution of a size can vary, one of the most common is a gelatine size. This type of size has been used for centuries, however, without additionally adding potassium aluminium sulphate (alum) it can deteriorate quickly. Adding alum to the size has become more of a recent addition and means that their is some control to the growth of bacteria which helps the ageing of the sheet.
There are also plant-based and synthetic alternatives, which makes the paper animal-free and something that you should keep an eye out for if you are a vegan, Hahnemühle is a brand that only uses synthetic sizing.
Sized Arches Pad
The key thing to remember is that for any type of sizing it improves printability, protects the sheet, gives the surface extra strength and makes the paper water resistant.