Facts About Processes, Pigments And Vehicles - A Manual For Art Students (1895) (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER II ON THE TESTING OF THE DURABILITY OF PIGMENTS BY EXPOSING THEM TO LIGHT AND AIR The durability of pigments depends on many conditions. They may be altered by contact with other pigments or by contact with impure paper, or badly-prepared grounds, or injurious media; they may be affected by special gases present in the atmosphere. These different causes of change we shall examine in due time. But in the majority of cases pigments yield simply to the action of light, air, and moisture. This gives us a very convenient method of applying a simple test to decide whether a pigment is durable or not. The action of air and moisture is enormously increased by exposing a pigment to a strong light. So much so that Captain Abney has calculated that two years' exposure to the direct light from out of doors is equivalent to four hundred years' exposure to the light of a picture gallery. Some realisation of the enormous difference between outdoor and indoor light may be obtained by noticing that a room looked into from the outside seems to be quite dark. By therefore exposingpigments to direct daylight, we can in a few months classify them, and separate those that are fugitive. I shall begin by describing how water-colour washes may be examined. This may be done by starting from the pigment as supplied in water by the artist's colourman, but it is better to prepare from the dry pigment, grinding it with a muller in water. Prepare some colour by grinding it on the muller with water, removing the paste to a little wide-mouthed bottle, and then adding a few drops of gum arabic solution. Common gum should, not be used, but some pure gum arabic should be bought at a chemist's, and then dissolved in warm water. This is best done by putting the gum arabic and the water in a bott...