Wallpapers

WALLPAPERS serve for finishing and decorating the interior walls of dwellings. W. penetrated into Europe from China; the first wallpaper factories appeared in England in the 18th century. The production of W. is essentially the production of paper (see Paper production), on which a certain pattern is then applied. Paper for W. is chosen dense, sufficiently well-sized; it is usually first coated with one color as a ground (cheap W. may also be without ground), after drying which the actual pattern is applied, sometimes with many colors. The work is usually done by machine. For cheap W., drying the pattern completes the production of W.; for more expensive varieties, satinizing follows drying, sometimes lacquering and other processes. Satinizing aims to give W. a shiny appearance, which is achieved by rubbing the front side with stiff hair brushes containing the finest talc until a gloss is obtained; sometimes the ground is also satinized. Lacquering achieves greater density of W., protects them from the action of dust and air, and sometimes even makes it possible to wash them. W. are also covered with oil or spirit lacquers containing in various combinations oil varnish, wax, copal, shellac and other resins. Special mention should be made of the production of velvet W., gilded, embossed, waterproof and fireproof; for the sanitary assessment of such varieties, it is important that W. are covered with thick boiled oil, varnish, glue, egg white with the addition of alum, ammonium phosphate, etc., i.e., W. are made even more impermeable. Papering walls, while serving to decorate dwellings, also has hygienic significance. The natural ventilation of dwellings, occurring through the pores and cracks of the wall building material and having importance for normal air exchange in rooms, depends to a large extent on the method of wall finishing. Plastering and painting with lime paint least hinder natural ventilation (air permeability decreases by approximately 25%; when covered with glue paint, it decreases by 50%, and when covered with oil paint, permeability is completely destroyed for the first years until small cracks form in the paint). Papering with wallpaper also reduces natural ventilation, but differently depending on 1) the thickness of the wallpaper paper, 2) the degree of their grounding, 3) the method of applying the pattern, 4) their variety (ordinary varieties less, satinized, lacquered and generally expensive varieties more hinder air passage) and 5) the material with which W. are glued (starch paste less, glue more). Research has shown that after wallpapering, a decrease in air exchange in the room is observed within the range of 18% to 75%. Expensive, very dense wallpapers on glue completely stop air exchange. Thus, in the natural ventilation of dwellings, W. play the role of a retarding factor. W. also affect the lighting of the room depending on their color. The darker the color of the wall finish, the more light is absorbed by the walls, and the less light is reflected from them. If white walls (whitewash, paint) absorb only 8% of the light flux and reflect 92%, then papering walls with yellow W. gives absorption of 60% and reflection of 40%, with blue W. absorption of 75%, and with dark brown W. absorption of 87-96% and reflection only 13-4%. Such an influence of the color of W. is generally the same for both natural and artificial lighting. To obtain the same degree of room illumination, 87 candles are needed for dark brown W., 72 for blue, 60 for light yellow, and only 15 for whitewashing with chalk. Over time, W. become dirty from soot, dust and dirt (this is especially noticeable on light W.), which also significantly reduces their light-reflecting ability: thus, depending on the degree of contamination, a loss of this ability is noted by 30-50% (yellow wallpaper clean reflects 40%, and dirty only 20%). Therefore, papering with dark wallpaper and heavy contamination of light wallpaper can significantly reduce the illumination of the room. When papering walls, the plaster is coated with a hot liquid solution of glue so that the paper does not separate from the top layer of plaster; to obtain a smooth surface, a layer of newspaper paper is often pasted onto the plaster, on which W. are pasted with starch paste, sometimes with the addition of glue for strength (dextrin or gum arabic is rarely used). Painter's glue is a cheap variety of carpenter's glue, light, dissolving in cold water and almost incapable of turning into jelly; such glue easily rots. If W. are pasted on damp walls or dampness appeared later, under the influence of bacteria and mold fungi, the glue and paste rot, as well as the decomposition of paints and binding substances (gum, dextrin, starch, glue, etc.). The odorous products of their decomposition, as well as the products of vital activity, mainly mold fungi, enter the room air and thereby spoil it. If W. contain even traces of arsenic, a garlic odor is observed. The cause of such air contamination from rotting W. is not difficult to establish if there is dampness on the walls: the walls are cold to the touch, W. form wrinkles, separate from the wall, change their color, spots appear on them from adhering dust and the growth of mold fungi (whitish, yellowish or greenish depending on the type of fungi), and with prolonged and severe dampness, W. can completely rot. Sometimes W. are not pasted on plaster, but directly on wooden walls, then under W. many spaces remain in which dust gradually accumulates, and in untidy dwellings, bedbugs and cockroaches breed. But even when pasting W. on plastered walls, insects easily breed under them; it is difficult and often impossible to free the room from them without removing the wallpapers themselves. Disinfecting W. is very difficult. The method of cleaning W. with the crumb of fresh wheat bread, mixed with water to obtain a very steep but not sticky, non-crumbly dough, proposed in Germany, has not become widespread in the USSR, and more often wallpapers are wiped with rags soaked in disinfectant solutions. Such disinfection is insufficient, while abundant spraying of W. with disinfectant solutions is impossible without damaging them. This also unfavorably distinguishes W. from whitewashed and painted walls, which are easily amenable to cleaning and disinfection or simply to secondary whitewashing. The most rational way to disinfect rooms with pasted W. is with formaldehyde: sulfur dioxide strongly damages the color of W. Recently, special varieties of W. with stable coloring have been produced, which can be washed, disinfected, and washed with brushes and soap (Salubra, Metallfolientapeten, Sigur, etc.). In view of the above hygienic disadvantages of W., papering schools, preschool institutions, dormitories, etc. should not be allowed. For coloring W., both mineral and organic paints are used, which must not only be durable in relation to light but also harmless to the health of residents. Therefore, some, although durable and beautiful, paints are prohibited by legislation due to their harmfulness. Of poisonous substances, lead is most often encountered, which is part of many paints, especially white and yellow (white lead, massicot, chrome, Cassel yellow, etc.), however, lead is rarely present in W. in significant, dangerous to health quantities. More frequent and more dangerous is the presence of arsenic in W. It is present in large quantities in green paint (Schweinfurt green or copper acetoarsenite), containing up to 58% arsenious acid. This paint is prohibited by law in the USSR. In addition, arsenic is found in many aniline dyes—into which it enters as a material for obtaining these dyes and remains as an impurity; finally, arsenious acid or sodium arsenate is used as a mordant when dyeing fabrics (a few milligrams per 1 m³). In both cases, there is little arsenic in W., especially in the mordant (according to German law, the content of arsenic up to 0.2 g per 100 g of paint and not more than 2 mg in 100 cm² of wallpaper is allowed). From W., arsenic can enter the air, and from there to a person and cause chronic poisoning in two ways: either the arsenious paint is rubbed off, and with it arsenic, which in the form of dust (arsenious acid) enters the air, or arsenic passes into the air when arsenic-containing paints on damp W. decompose, when certain molds develop on these W. and arsenic-containing paints: Aspergillus niger, Penicillium glaucum, Penic. brevicaule, and arsenic passes into the air in the form of highly poisonous arsine (AsH₃), which has a characteristic garlic odor (according to new research, this is not arsine, but cacodyl oxide [(CH₃)₂As]O). Prolonged stay in such rooms can cause chronic arsenic poisoning (see). Therefore, paints containing significant amounts of arsenic are prohibited for coloring W. Testing W. for lead is rarely done, much more often for arsenic.

Lead is determined in the ash of wallpapers—after dissolving it in HCl and treating it with H₂S, it is detected in the form of black lead sulfide, insoluble in weak acids and alkalis, or in the form of yellow lead chromate from treatment with potassium dichromate. Wallpapers with a significant amount of arsenic, when burned on a candle, give a characteristic garlic smell. The usual method for determining arsenic is in Marsh's apparatus, where when sulfuric acid and zinc act on arsenic wallpapers, arsine is formed, which gives an arsenic mirror on a narrow glass tube or on a porcelain plate. A simpler method is Gutzeit's method: in a small flask, wallpapers are treated with sulfuric acid and zinc; arsine is formed, which on a paper applied to the neck and moistened with a saturated solution of silver nitrate gives a lemon-yellow spot (Ag₃As), which soon turns black.