Whether you’re a seasoned watercolour painter or new to the discipline, knowing the most important watercolour surface terminology will ensure you choose the ideal surface for your work.

Be sure to bookmark this page, your go-to glossary of watercolour surface-related terms.

Acid-free

Produced by using cotton linter or wood-free fibre, acid-free paper is pH neutral, which is essential for the long term stability of paper.

Buffering

Buffering allows a sheet to counteract atmospheric acidity over time. It is achieved by adding an alkaline filler such as calcium carbonate to the sheet at the pulp stage.

Colour

Watercolour papers are traditionally white, allowing the maximum amount of light to be reflected back through the wash. Conversely, tinted papers give a mellow tone to a painting (see the visual example below).

Deckle

A deckle is the frame which is used to make paper. “Four deckle edges” is a common phrase which indicates that a sheet is mould-made, simulating the look of handmade paper (see “mould-made paper” below for more information).

External sizing

This refers to a layer of gelatine on the surface of paper which means watercolour film can sit atop it, will look brighter, and can be sponged off by the painter.

External sizing is also known as gelatine surface sizing and creates a harder surface, which allows scraping and rubbing without damaging the paper itself.

 

Internal sizing

Internal sizing reduces the absorbency of paper fibres by chemically bonding to them.

Mould-made paper

Some paper is formed with a cylinder mould. Fibres are arranged at random to mimic a handmade sheet, and the arrangement provides dimensional stability, reducing cockling (wrinkling).

Rag content

100% rag means paper is made from 100% cotton. Here, the term rag dates to an era when old rags were used in handmade paper mills.

Today, the cotton used in papermaking still comes directly from the plant and is called cotton linter, whereas “wood-free” paper is made from chemically processed wood pulp and produces an acid-free sheet that is less costly than cotton.

The “right” side

The right side of paper is the side from which you can read the watermark. While either side can be used, painting on both sides isn’t recommended.

 

Surface: rough

This is the heaviest texture of paper. It is embossed from the surface it’s pressed between when the sheet is being dried, and is used by watercolour artists who rely on a more textured surface.

Surface: not or cold pressed

Not or cold pressed paper is a rough sheet which has been cold pressed to flatten out the texture. It is the most popular texture among watercolourists.

Not paper often produces the brightest watercolour paintings because its increased surface area holds more colour and therefore reflects more light.

Surface: hot pressed

Illustrators and miniaturists use hot pressed papers; a smooth paper finish blends with their images more comfortably.

Pastel papers tend to have a “grained” surface, which helps to hold pastel or charcoal on the paper. Printmaking papers tend towards the smooth end of the scale.

Watercolour blocks

Watercolour blocks consist of several paper sheets of paper, glued around all four edges to keep them flat while painting and eliminating the need to stretch paper before painting. A small section is left unglued to enable a palette knife to remove the finished work, one sheet at a time.

Blocks are excellent for painting en plein air – read more of our plein air painting tips here.

Weight

Heavier paper is more resilient to wear and tear, as there is more interwoven fibre in a heavy sheet. Lightweight papers should be stretched if you expect to use lots of water.

Many watercolourists prefer heavier papers as they are able to take heavier washes without cockling (wrinkling).

Weight measurements: imperial and metric

The imperial weight of a given paper is that of 500 imperial sized (30″ x 22″) sheets of that paper. So a lightweight watercolour paper might be 90lb. The metric weight is in grams per square metre (gsm), so a 90lb paper is equivalent to 190gsm.

NEW VERSION:

Imperial measurements tell you how much 500 sheets of the paper measuring 30″ x 22” weigh, in pounds. The metric weight is given in grams per square metre (gsm). A lightweight watercolour paper might be 90lb – equivalent to 190gsm.

 

Looking for more information about how to choose a surface for watercolour? Read our guides on the top three things to consider, and how how to stretch watercolour paper.