Paper is cellulose fibres derived from wood, rags, grasses or other plant sources that have been treated in water before being pulped and formed into sheets. However other ingredients such as pigments, dyes, buffers and size are also often added to produce papers for art that look and behave how you might want them to for centuries to come. Here, we list the ingredients you can expect your fine art paper to be made of, and explain why a quality art paper can only be made with the highest grade ingredients and production methods.
Fibres Used in Papermaking
The base ingredient of paper is cellulose fibre (with the exception of synthetic papers). So what are the differences between the various fibres and the papers made from them?
The wood used to make artist paper is a combination of both hardwood and softwood. Softwood trees tend to be evergreens, with needles rather than leaves, and include Pine, Spruce, Cedar and Fir. Hardwood trees tend to be deciduous broadleaf trees, such as Maple, Elm, Birch, Aspen and Poplar. Where softwood trees produce comparatively long (approximately 3.60 mm long and 0.035 mm wide), soft fibres that help with the paper’s strength, hardwood trees offer fibres that are shorter and narrower, denser and comparatively bulkier. The combination of the two types of wood offers the best of both worlds; strength and bulk. Artist papers tend to contain more softwoods than everyday papers because it offers a greater degree of surface strength. Paper is usually made with fast growing trees to make it as sustainable a material as possible. Many papers will have the FSC mark to indicate the sustainability of the wood used, however it is not an automatic accreditation and so not all sustainably sourced papers will show the badge on their paper.
In order for the wood to be usable for papermaking, it first has its bark removed, and then is turned into chips which are made by grinding with a rotating grindstone. These are then cooked in an alkaline solution in order to remove as much of the lignin as possible. This is the acidic content of the wood which is a vital component of the plant in life, but in the papermaking process needs to be removed as it would cause the paper to yellow and become brittle over time. Unfortunately not all the lignin can be boiled away like this, as this would also break down too much of the cellulose fibres needed for the paper. Instead buffers are added, which neutralise the remaining acidity in the paper pulp. This process is known as chemical pulping, and contrasts with mechanical pulping, the lower cost alternative used to produce papers that yellow quickly over time because of their acid content, such as newsprint.
Fine art wood papers are used for both drawing and painting media, and while being acid-free they are generally not considered fully archival because they have had to undergo chemical pH neutralisation.
Cotton rag refers to 100% cotton textile remnants used to make paper. The availability of cotton textiles that can be used for this purpose has decreased as more synthetic fibres are used in textile production, which are unsuitable for papermaking. Cotton rag fibre is considered stronger than wood-based fibre or cotton linters because it is longer, which means it has greater ability to form a tighter weave when pulped. It is also better able to withstand changes in temperature and humidity, giving it the potential for a considerably longer lifespan than wood-free papers. In order to make paper from cotton rags, impurities (such as buttons and zips) need to be removed before they are cleaned, shredded and pulped in order before being set into sheets. Cotton is naturally acid-free and so alkaline buffers such as calcium carbonate are not required.
Cotton linters are the fine fibres left attached to the seed after the ginning process (as a matter of interest, ‘ginning’ derives from ‘cotton engine’ and is the machine used to separate the cotton from its seed so it can be used to make cotton thread for textiles). The fibres that are still stuck to the seed after ginning are shorter and so therefore the paper made from cotton linters tends to be less strong than cotton rag papers. However, that said, high-quality cotton fibre paper is known to last hundreds of years without fading, discolouration, or deterioration, and is therefore a very popular surface for fine art applications. Many fine art papers use a combination of cotton linters and cotton rag, in order to make a robust, long lasting paper that is less expensive than a 100% cotton rag paper. Cotton linters are also sometimes blended with woodfree cellulose to make good quality fine art paper for dry and wet media.
Linen rag was the predecessor to cotton rag in papermaking. The remnants of linen textile were first used to make paper in Europe in the thirteenth century, although there is evidence of linen fibres being used in papermaking that date back to as early as 960 A.D. Arabia. Linen fibres, derived from the flax plant, are very long and strong. However their availability is limited and so it is comparatively very expensive. Today linen is only used in a few papers, and is often combined with cotton rag or cotton linters.
Bamboo fibre has been used to make paper in China for thousands of years, and high-quality, handmade bamboo paper is still produced in small quantities, particularly for printmaking. Bamboo papers are mainly produced in China, Myanmar, Thailand, and India. Bamboo is a very fast growing plant and as a result bamboo paper is considered highly sustainable. Bamboo papers are suitable for a variety of media including sumi-e, graphite, charcoal and printmaking.
The term ‘rice paper’ is a bit of a misnomer. Rice paper for fine art applications is either made from the pith of a small tree, Tetrapanax Papyrifer, or from the bark fibres of the mulberry tree. Tetrapanax Papyrifer, or ‘the rice paper plant’, is indigenous to the swampy forests of Taiwan and Southern China. It is made into paper by stripping the boughs of the tree of its bark, and then extracting the white pith from the rest of the plant stem. This white pith is then swelled with water and then dried, before being sliced with a knife to produce a continuous sheet. The resulting paper has a fine ivory like texture that is not suited to being used as a writing surface, but was popular for watercolour and gouache in 1900s Europe. Unlike paper made from a pulp, ‘pith paper’ (as it is most accurately known) maintains aligned plant cells from the tree’s natural state. As a result of this watercolours and gouache works made on pith paper require specialist treatment in conservation, and are particularly sensitive to changes in atmospheric humidity.
On the other hand, mulberry paper is stronger than wood cellulose paper. It is made by stripping the bark from the mulberry tree in autumn, cooking it in a solution of water and soda ash before the fibres are carefully prized apart by hand to ensure their lengths are maintained. Following this process the inner bark fibres are then pulped and formed into sheets. Different types of mulberry tree produce different papers, such as gampi, mitsumata and kozo, all of which are popular relief printmaking papers.
Synthetic fine art papers are made from heated polypropylene pellets which are then extruded to form the base and surface layers of the paper. The resulting paper is opaque, very smooth, and tear and buckle-resistant, though similar in appearance to regular smooth paper. It is also possible to produce clear synthetic paper which can be useful in creating works of art intended to be backlit. As the paper is completely non-absorbent it is more important than with natural cellulose-based paper to spray finished works with varnish to ensure it remains stable.
It is very easy to contaminate paper pulp and so it is vital for paper makers to use the purest available water to avoid this from happening. Many paper mills are situated by natural lakes and rivers to make use of the readily available water supply, often naturally filtered through limestone.
Calcium carbonate (chalk) is alkaline and is added to groundwood-free, wood-based pulp in order to act as a buffer and neutralize the acidity of any remaining lignin following cooking the wood. This also helps to reduce the dark brown colour that lignin gives the paper pulp, making the final paper whiter. Additionally, Calcium carbonate also makes the paper smoother and more opaque. calcium carbonate also aids the binding of the fibres in the pulp, however too much can reduce the tear strength, burst strength and tensile strength of the paper. Talc and china clay are alternative ingredients to calcium carbonate, and are able to fulfil a similar role in papermaking.
Pigments and Dyes
Both pigments and dyes are known to be used by some paper manufacturers to colour papers, with pigmented papers being more resistant to the harmful effects of UV light than dyed papers. However if the paper is coloured in manufacture, how it is fixed to the pulp is of equal importance to the quality of the pigment or dye being used. Most coloured papers use a synthetic fixing agent to help with the retention of pigments and dyes. Titanium dioxide has been added to some papers to make it appear whiter without the use of OBAs (optical brightening agents), however it is very expensive and can also impact upon the strength of the paper. For this reason it tends to only be used in heavier weight papers.
Optical Brightening Agents
OBAs are additives added to the pulp in order to produce a whiter paper. They absorb light in the ultraviolet and violet region and re-emit light in the blue region, creating the illusion that the paper is whiter than it is. Unfortunately OBAs have a limited capacity and over exposure to the UV rays of natural daylight will eventually cause the OBAs to stop functioning. It is generally thought that papers that contain OBAs are not archival. If you were to take one piece of paper which contained OBAs, and one that did not, into a dark room with a UV blacklight, the paper with OBAs would glow while the ‘optically dead’ paper would not. So, while whiter paper may hold more appeal at first glance, two advantages of fine art paper that does not contain OBAs is that it is more likely to be archival, and it will not change its appearance under different lighting conditions, thus remaining more constant.
The amount of size used in paper-making will alter the absorbency of the paper. Unless the paper is waterleaf and completely absorbent (like blotting paper), most fine art papers (both soft sized which is quite absorbent i.e. most cotton and wood-based relief print papers, and hard sized, which is much less absorbent, i.e. the less absorbent watercolour papers) will have a degree of internal sizing. This is usually made of methylcellulose or alkyl ketene dimer (AKD), both low cost and readily available. External sizing is when the formed paper sheets are soaked in a tub of gelatine (made from animal bones and hides), modified vegetable starch (potato, rice or wheat) or acrylic co-polymer to form a water repellant film on the surface of the paper.