There are three ways to make watercolour paper, each method influences the properties of the paper along with the quality of the raw materials used usually Hand-Made and Mould Made papers are the best quality, mainly because it makes no sense to make low quality paper with such a high labour cost. Handmade paper is usually inconsistent from sheet to sheet unlike Machine made
Cellulose fibres (mainly from the cotton plant but can also be jute, hemp or wood pulp) are ground up and mixed with water. This mixture of fibres and water is called pulp.
After the pulp is made It is passed into a vat and agitated mechanically to give an even concentration. The papermaker stands by with a pair of moulds (a wooden frame covered in a fine wire mesh). The mold is the dipped into the pulp and lifted out with a shaking action by the papermaker. The water drains off leaving a matt of fibres in the mould.
The outer edges of the mould are covered by a removable frame during this operation which is called a deckle. The edge of the sheet is at the deckle, but one gets fibre seepage under the deckle. Thus the edge of the sheet is not a sharp edge, but a rather ragged gradation down to nothing - this is called a deckled edge and is the natural edge obtained when paper is made by hand. Because of the method of manufacture, the fibre orientation is random and there are no significant differences in properties of the sheet in the long or short direction.
Mould Made Paper
Using the same pulp and raw materials as the handmade paper. At the point of manufacture, the process is now automated, and the pulp is passed into a vat that contains a rotating cylinder (Called a Cylinder Mould) partly immersed in the pulp, again like the handmade method is covered in a fine wire mesh. As the cylinder rotates, the fibre forms into a matt on the outside of the cylinder. Just after the highest point of rotation and before re-entering the vat, this matt of fibres is couched off onto a felt and removed continuously from the point of manufacture to be further processed. Because of the nature of the machine, there are usually very slight differences in the long and short directions on each sheet.
Machine Made Paper
Using a principle developed by the Fourdrinier brothers (hence why the machine is called a Fourdrinier machine), this machine gives the most economical production when producing paper at a high speed. The same materials and pulp are used but this time with a lower concentration of water. Commonly, but not always with machine-made paper, the pulp is of lower quality than for either of the above. This is now passed onto the Fourdrinier machine a horizontal fast-moving wire mesh that the excess water drains through, leaving the sheet formed on the wire.
Paper today is referred for as GSM (Grams Per Square Metre) the lower the GSM the lighter the paper, Typically the most popular weight of paper used is 300 GSM
HP = Hot Pressed (also known as smooth, satine or silk) – Pressed between two hot plates to create a smooth paper – Suitable for high detail work
NOT = Not Hot Pressed (also known as cold pressed, Fin or CP) – A Matt, Smoothish/Roughish paper – Suitable for most types of work, the most popular surface of paper
Rough = Rough (also known as torchan) – A rough textured paper – Suitable for textured work, landscapes or seascapes
A term used on some of the finest papers to slow down degradation and stop yellowing
Sheets/rolls – Traditional watercolour paper usually with 2-4 decked edges
Blocks – Pre stretched paper, glued on all four sides to prevent warping of the paper whist painting
The highest quality papers usually contain Cotton offering the best archival standard and durability with the cheapest more student quality papers being made from wood pulp confusingly call wood-free
Extra white or High White papers usually have a little bleach added into the manufacturing process sometimes with titanium dioxide pigment, even when this is done the paper is still not truly white and will have a slight creamy colour to the paper