Paper, Vellum, Parchment,
and Ivory

As paper is used as the painting-ground for the vast majority of works executed in water-colours, and as this method of painting offers but slight protection to the pigments employed against hostile influences, it becomes of the greatest importance to ascertain that no unnecessary elements of danger are introduced in the paper itself. We will now proceed to consider briefly the sources and constituents of drawing-paper.

Linen from the common flax [Linum usitatissimum], and in the form of white rags, should be the basis of the pulp used in the making of sound drawing-paper. In actual practice the cheaper and weaker fibre of cotton [seed-hairs of Gossypium sp.] has almost entirely displaced flax, although during recent years a successful attempt has been made in England to produce a high grade of hand-made drawing-paper almost wholly composed of linen. Other vegetable fibres might, no doubt, be employed for this purpose. Thus, Japanese paper, prepared from the bast-fibres of the paper-mulberry [Broussonetia papyrifera], were it made less absorbent by the introduction of a sufficiency of size, would probably become an efficient, strong, and durable substitute for linen-paper; but at present linen-papers, cotton-papers, and papers made from a mixture [p. 7] of these fibres, are the only kinds with which water-colourists are practically concerned.

During his explorations of Chinese Turkestan, Sir Aurel Stein recovered many examples of early manuscripts written on felted vegetable fibre, that is, paper. In the British Museum are two scraps of such paper, with Chinese writing, which must be dated somewhere between the years A.D. 25 and 220. They are the most ancient specimens of paper known to exist in the world. But the manufacture of linen-paper in Europe has not at present been traced back farther than the second half of the twelfth century. Mr. W. H. James Weale, formerly Keepr of the Art Library in the Victoria and Albert Museum, informed me that ^the two first paper-mills in France were set going near Ambert, in the valley of the Valeyre, by men who, during their captivity in the Holy Land, were forced to work at the manufacture of paper at Damascus. One of these French mills was called 'Damascus,' the other 'Ascalon.' This was previous to the year 1189. To Mr. Weale I am also indebted for an opportunity of examining two early specimens, obtained from the 'Registre des Revenus de l'Évêché du Puy.' As one of the sheets contains contemporary entries of the year 1273--the other entries belonging to 1289--these papers are, at least, as early as the years named. Both papers present the creamy hue, the translucency, and the gloss of vellum. One hundred square inches of the earlier specimen weigh 127 grains; of the later, 163. Both are heavily sized with paste made from wheaten starch. The use of starch for sizing paper has been revived as of recent years, but animal size or jelly is still extensively employed. Some paper is, indeed, made from felted linen pulp alone without size; but it is blotting or filter paper, and is quite unfitted for [p. 8] water-colour work, for when a wash of pigment is passed over it, the colouring matter and the water partially separate, while the outline of the brush-stroke is not preserved.

Before entering further into the question of what are the essential and what the accidental and unnecessary constituents of paper, I give the summarized results of six analyses, which show the percentage proportions found in good samples:

ANALYSES OF DRAWING-PAPERS
Paper			Water	 	Size		Ash	 	Fibre
Hodgkinson, 1869	6.8		4.6		1.1		87.5
English, 1876		10.9		6.1		1.1		81.9
Dutch, 1876		11.0		4.8		0.9		83.3
Whatman, `1885		7.4		6.3		1.1		85.2
Arnold, 1894		7.4		7.6		1.5		83.5
'O.W.,' 1897		8.7		5.5		1.7		84.1

Water. It should be noted that the percentages of water shown in these analyses vary considerably be reason of variations in the humidity, temperature, and pressure of the atmosphere to which the different papers had been exposed just before the analyses were made. There are, however, slight permanent peculiarities in samples made from different fibres or sized in different ways; in consequence the moisture-absorbing and moisture-retaining properties of different papers are not precisely identical under identical atmospheric conditions. This hygroscopic moisture does, indeed, vary inversely with the temperature, and directly with the amount of water-vapour in the air; it is increased also by an increased barometric pressure. There is no doubt that if it could be wholly excluded, the larger number of changes which occur in the pigments of a water-colour drawing would be prevented. It is most injuriously active when a framed drawing is exposed to considerable [p. 9] ranges of temperature. Under these conditions the moisture of the paper is first partly turned into vapour, then condensed on the glass, and, lastly, is re-absorbed by the paper, and, for a time, specially by the pigments lying on its surface. This temporary condensation of an excess of moisture upon the coloured surface does much injury before hygroscopic equilibrium is once more re-established. Much less harm would accrue were the vaporized water allowed to escape.

Size. The size must be considered next. It may be applied to the pulp or to the sheet, and may consist of gelatine with a little alum, or colophony or rosin dissolved in soda-lye, followed by treatment with alum or alum-cake. Sometimes starch is used along with alum or alum-cake. From good drawing-papers, which are sized in the sheet with animal size, the greater part of the size may be extracted by means of boiling distilled water, the solution being usually neutral or faintly acid, sometimes faintly alkaline, to test-papers. Gelatine and starch, to the extent of about 5 per cent. of the weight of the paper, are the safest sizing materials.

Ash. The ash or mineral water in paper may be derived from three sources, namely, traces of the original mineral substances taken up by the flax plant from the soil, and still remaining associated with the felted pulp; the mineral matters, such as soda and alum, introduced with the size; and, lastly, the mineral compounds used to whiten, to weight, or to finish the paper, or in bleaching the fibre and as 'antichlors.' In common and adulterated papers the ash greatly exceeds 1 per cent., twelve parts per hundred of paper being no unusual proportion. This 'filling' may contain or consist of the following substances: kaolin or china-clay, silicate of lime or 'pearl-hardening,' chalk or [p. 10] whitening, lead-white, baryta white or 'white dressing,' artificial gypsum or 'satin-dressing,' and a mixture of aluminum hydrate with magnesium carbonate or with calcium carbonate, known as 'satin-finish' or 'satin-white.' Other substances which increase the amount of ash left when a paper is burnt are blue colouring matters, introduced to counteract the natural yellow tint of the pulp. These include artificial ultramarine, smalt or cobalt blue, and Prussian blue.

Fibre. What is put down as fibre in the analyses of paper previously cited, is a substance, or group of substances, to which the name of cellulose is given by chemists. Cellulose consists of the three elements--carbon, hydrogen, and oxygen; it is, when pure, entirely combustible, leaving no ash.

The source of this cellulose is by no means without influence on the durability, strength, and working quality of drawing paper. The fibres of linen and of cotton present distinct differences of form and resistance to strain. When working on a paper with a knife so as to develop high lights, the water-colour painter soon discovers the weakness and fluffiness of abraded cotton, while the clear-cut surfaces of linen are equally obvious. Even in washing and in taking out lights from a drawing by sponging and rubbing, the superiority of linen paper to cotton-paper is very marked; in fact, papers into which a high proportion of the latter fibre enters will not stand much worrying. The other fibrous materials commonly forming the basis of ordinary papers are, on one score or another, less desirable than cotton. Nearly all of them require, in order to fit them for paper-making, a very drastic treatment, which is liable to leave behind it traces of injurious chemicals, or to yield altered material of lessened strength and permanence. [p. 11] Wood-pulp, esparto, and straw-pulp belong to this category.

Paper-making. The technology of paper-making cannot be discussed here, but a few references to the chemicals employed in the process of manufacture may be usefully given at this point. Amongst these chemical substances, one or more of which will have been introduced into the fibrous basis of the paper or into the size may be named: caustic soda and caustic lime; chloride of lime, magnesium hypochlorite, moist chlorine gas, and sulphuric acid; alum, aluminium chloride, and aluminium sulphate; sodium sulphite; gelatin. Of course, it is possible to cleanse and bleach the higher class of rags without having recourse to any chemical treatment, but the 'souring' with sulphuric aid and the employment of some soda or sodium carbonate to remove grease are usual; while there is always a salt of aluminium present in the size. Indeed, in the best and purest drawing-papers, the alum, or its equivalent, is the one ingredient upon which the chemist interested in paintng will look with suspicion. But the subject of the presence of chemicals, injurious or innocuous, in the finished product of the paper-mill may be relegated to the following paragraphs.

Paper-testing. The simplest test of the suitability of any sample of drawing-paper for water-colour work consists in applying to its surface uniform and weak washes of a chosen set of sensitive pigments. A sound standard paper is taken for comparison; this may be 'Whatman,' but it should be first swelled in cold distilled water for five minutes, and then hung up to dry. In applying this test, a strip of the sample to be tested and one of the standard paper should be laid side by side, and then the several colour washes, made with distilled water, carried [p. 12] across both strips by means of a broad brush. The pigments used may be French ultramarine, chrome yellow, and carmine. Unless they are employed in very dilute admixture, the changes produced by alum and other chemical will not be perceptible. There should be no bleaching of the ultramarine or the carmine, or any blueing of the latter, and no dulling of the chrome, even after the lapse of a week from the date of the experiment. Washes of tincture of azolitmin from litmus, tincture of dahlia flowers, and tincture of methyl-orange may be similarly applied to paper-strips; in this case it will probably be found that the two former tests will show an acid reaction, and the methyl-orange a basic or alkaline reaction. This seemingly strange result has been found to arise form the presence of a derivative of the alum in the size, namely, an aluminium sulphate which is acid to some tests and basic to others. This point has been established by the experiments [Journal of the Society of Chemical Industry (1892), pp. 212, 213, 216.] of Messrs. Cross and Bevan, Mr. C. Beadle, and Drs. P. N. Evans and Quirin Wirtz, who have proved that all the drawing-papers of well-known makers which they have examined contained no free sulphuric acid. Of course, the question remains, 'How far if at all, is the basic aluminium sulphate in drawing-paper injurious to sensitive pigments?' This inquiry can, I think, be answered by applying the colour-tests already described, not only to the suspected papers themselves, but also to extracts from them made with cold distilled water and also with hot.

Other useful tests are the following:
1. Burn 100 grains of paper to a white ash; not more than 1.5 grains of incombustible residue should be found.

2. Extract 100 grains of paper repeatedly with boiling [p. 13] distilled water. The united watery extracts, evaporated to dryness, should not amount to 8 grains.

3. If straw or esparto fibre be present in a paper, it will become red when immersed in a boiling 1 per cent. solution of aniline sulphate.

Attempts have been made to size paper with casein dissolved in ammonia, and also with 'viscose,' a modified cellulose made out of the substance of the paper itself by means of water, caustic soda, and carbon disulphide. At present, however, gelatin-sizing holds its own. The necessity of introducing alum, or an equivalent of some other aluminium salt, into this size is its chief drawback, although an animal product of the group to which gelatin belongs, being prone to decomposition and to the attacks of microscopic organisms, itself constitutes a source of danger. Alum is used not merely as an antiseptic, but because it exerts a peculiar liquefying effect upon the size. A little alum solution added to gelatin solution increases its stiffness, but further additions up to an easily ascertained point make the solution more mobile. It is absolutely necessary to keep the alum percentage low; I found in a batch of one-well-known make of drawing-paper that exactly twice as much alum had been employed as was necessary. My remonstrance with the manufacturers had its due effect.

The roughness or smoothness of the surface of the paper, or cardboard, is not without influence on the permanence of water-colours. The pigments become less intimately associated with the smooth surface of a hot-pressed paper than with a comparatively rough natural surface. The rough surface is, however, liable to wider and more rapid fluctuations in the amount of hygroscopic moisture.

Some apparently sound papers deteriorate in strength and tint on being kept. Such changes may occur even when [p. 14] pure linen rages have been used for the pulp; they may be generally traced to the disintegrating action on the fibre of the chemical bleaching agents employed. The development of rust-posts, when not due to the mount or backing of a drawing, arises from the presence of small particles of metallic iron from the machinery having become embedded in the pulp. These particles appear grey, brown, or black; they may be detected by placing a drop of oxalic acid solution on the unsuspected spot, allowing it to dry, and then moistening the place with a drop of a freshly-prepared solution of tannin. If the particle be iron an ink stain will be produced. However, some dark spots consist of blackened grease, or of tar, or of the paper-fungus [Myxotrichum chartarum].

Naturally, there is a small quantity of 'oil' or 'fat' in paper; it varies from 3 to 5 parts in a thousand. The difficulty experienced in immediately wetting a surface of paper, caused by the presence of this trace of oil, may be overcome by first washing the surface with distilled water to which a drop or two of caustic ammonia has been added. A solution of the natural mixture of alkaline organic salts, known as oxgall, effects the same purpose. The use of borax had better be avoided. It is always advisable to wet the whole surface of the paper before beginning a water-colour drawing. Thus any abrasions or defects of the surface will become apparent.

As drawing-papers are sized in the sheet they occasionally show a peculiar defect arising from the irregular distribution of the size. In such cases, when the surface is scraped off, an absorbent layer of imperfectly sized pulp is revealed beneath . When such paper is used for water-colour painting the sinking-in and running of the pigments produce disastrous results; but it is easy to guard against [p. 15] accidents of this sort by previously scraping and colouring a corner of the sheet to be used. The peculiarities generally owing to the too prolonged and low drying of the sheets of paper after they have been removed from the warm sizing-bath and pressed. The solution of size is brought to the surfaces from the interior of the sheet, and remains there. Moreover, in very slow drying, the size is apt to decompose with loss of its glutinous character and, possibly, the formation of mildew. A good drawing-paper will indeed have rather more size at the surface than in the interior, this result being secured by a rate of drying which is neither too rapid nor too slow. Let us add that the strength of paper when completely wetted and in the presence of free water, is very low. If, however, it has been gelatin-sized and afterwards sprayed with a 40 per cent. solution of formalin to coagulate the gelatin it becomes appreciably stronger.

As to vellum, parchment, and ivory, little need be said. All three contain the characteristic ingredient ossein, an insoluble nitrogenous organic substance, which by long boiling with water is converted into gelatin: a solution of gelatin constitutes ordinary size. Water-colour paints placed upon any of these materials sink either very slightly, or not at all into their substance--a very few, such as aureolin, strontia-yellow, and madder carmine, stain the superficial layer. The old method of preparing vellum for the reception of water-colours consisted in rubbing the surface with very finely-ground bone-ash, or with pulverized sandarac. Pumice-stone or cuttle-fish, reduced to a minutely divided state by pounding, grinding, and sifting, may be used for this purpose; the infusorial earth known as polishing silica, or kieselguhr, may also be employed. [p. 16]

Ivory which as become yellowish through age and seclusion from light may be safely bleached by contact with an ethereal solution of hydrogen peroxide. The treatment is best carried out on a wide-mouthed stoppered bottle, care being taken to immerse the sheets of ivory wholly in the liquid, and not to allow them to touch each other.

Much care is necessary in selecting tinted and coarse coloured papers for water-colour work. The tints of the former are often obtained by the introduction of fugitive pigments into the pulp; the latter are often made of inferior and mixed fibres, and sometimes contain lead-white and other injurious fillings. [Turner' paper, for example, owes its grey-blue tint to the presence of indigo, while 'Varley' paper contains about 20 per cent. of 'mechanical' wood pulp, a material which steadily darkens into brown after but a short exposure to light. 'Sugar' paper, whatever its hue, should be avoided. Mill-board is often made of wood-pulp, oakum and straw-pulp: its surface is primed for oil-painting in the same was as canvas. [pp. 7-17]