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ENTERTAINING EXPERIENCES AT HOME
Watercolor paints. Chemical experiments
Entertaining experiences at home / Chemistry experiments for children In old books, the names of exotic dyes are often found: red sandalwood, quercitron, carmine, sepia, logwood ... Some of these dyes are still used today, but in very small quantities, mainly for the preparation of artistic paints. After all, natural dyes with such beautiful names are obtained from plants and animals, and this, as you understand, is expensive and difficult. But natural dyes are very bright, durable, lightfast. It would be interesting to check. But how? Kampesh tree grows in South America, sandalwood - in South Asia, sepia is extracted from cuttlefish, carmine - from cochineal (tiny insects) ... And yet it is quite possible to obtain natural dyes even at home, even in the middle zone of our country. And in the plants familiar to us there are coloring substances, albeit not so bright and not so persistent. Our ancestors often used them. We will also try to extract dyes from plants, and then on their basis we will prepare water-soluble paints, known to everyone as watercolors. Naturally, the dyes that we will finish should be well soluble in water. We will prepare all dyes in the same way: grind the plants or any of their parts and boil for a long time in water to make a concentrated decoction. It should be thick enough. We do not need to extract the dry dye - anyway, we have to prepare a water-soluble paint. A very important note: take only those plants that are allowed to be collected where you live; in no case do not tear plants taken under protection in your region or republic. And in any case, in order not to harm nature, limit the number of plants collected to a minimum. Let's start with red dye. It can be obtained from the stem of St. John's wort (the decoction must be acidified) or from the root of the bedstraw. You may not know what these plants look like. In this case, consult a biology teacher or take some reference book or plant guide from the library; they, as a rule, give both descriptions of plants and their drawings. Alder bark put in water for a few days, and then prepare a decoction. Again you will get red dye. It can also be extracted from the roots of horse sorrel, but in this case, do not forget to add a little aluminum alum to the finished broth - otherwise the color will be dull. From the roots of the famous elecampane plant (it, like St. John's wort, belongs to medicinal herbs), you can get a blue dye. To do this, the roots must first be held in ammonia - an aqueous solution of ammonia. Blue dye can also be obtained from larkspur flowers and buckwheat roots. The green dye is extracted from the leaves of the shamrock (also, by the way, a medicinal herb). Not so bright, but nevertheless a beautiful gray-green dye you will get from the leaves and stems of the cuff; before preparing the broth, they must be thoroughly crushed. Yellow dye is given by many plants: dyeing gorse, hazel (bark), alder buckthorn (bark, leaves, berries), bedstraw (flowers). From the fruits of barberry, a yellow dye with a lemon tint is obtained. If you boil the dry peel of onions in water, you get a brown dye of different shades - from almost yellow to dark brown. Another source of such a dye is the dry bark of the joster. Blueberries and blackberries, as you might guess, contain a purple dye. It is not very resistant, but may well be useful for watercolors. And from the stems and leaves of celandine it is possible to extract an orange dye. How to get black pigment? Firstly, for this you can prepare a decoction of berries and crow roots. But there is another, simpler way: add iron sulfate to one of the decoctions obtained earlier. Almost all of our decoctions contain tannins like tannins (remember the experience with tea), and in the presence of ferrous salts they turn black. Have you stocked up on enough thick multi-colored decoctions? Then let's get down to the main thing - the manufacture of watercolor paint. Its main components are dye and water, but there are other essential components. First of all, substances that bind paint to paper, such as gum arabic or wood glues, are substances with increased stickiness. Further, viscous substances are needed, they will prevent the paint from spreading over the paper, making it lie in an even layer; honey, molasses, glycerin are good for this. And the last additive is an antiseptic and disinfectant. After all, we are dealing with substances of plant origin, and they must be protected from the action of microorganisms (mold fungi, which will certainly want to feed on our paints). If you do not have gum arabic, then it is best to take cherry or plum glue as an adhesive, smudges on the trunks that can be collected directly from the trees - this is not harmful to them. True, such glue (more precisely, gum) dissolves in water with difficulty, but if you add a little acid, the dissolution will go much faster. For paint of each color, prepare 5-7 ml of an adhesive solution of approximately 50% concentration. Mix it with an equal amount of glycerin or about a third less honey. Phenol will serve as an antiseptic, its 5% solution called "carbolic acid" is available in pharmacies. This substance needs very little, just a few drops. Mix all the components of the future paint. The base of the paint is ready, only the most important thing is missing - the dye. Add it last as a thick decoction, taking about the same amount as you got the base for the paint. Here, in fact, is the whole procedure. You may be wondering why the paint is not solid - in stores it is sold in tiles. However, artists also use semi-liquid watercolors, in tubes. By consistency, they just resemble those multi-colored paints that you just prepared. If you are going to store your paints, be sure to transfer them to some kind of bottles with tight plastic stoppers, otherwise the paints will dry out soon. And you need to work with them in the same way as with any other watercolor paints: a soft brush, thick paper ... However, among the young chemists, there are certainly young artists. Before moving on to a new topic, here's one more piece of advice: try dyeing the fabric. Indeed, in the old days, most of the vegetable dyes were used for this purpose. Let's just agree on this: do not put good things in the dye bath (and it can serve as a bowl or basin). Experiment first with pieces of clean white fabric or yarn. And only in the event that you are convinced that the experiment is successful, take some thing - be sure to from the same fibers on which you set up the experiment. Before dyeing, the fabric, as a rule, needs to be pickled - held in a hot solution of some salt; for this purpose, a solution of potassium alum is often taken. After holding the fabric or yarn in the mordant for several minutes, dip it into the dye broth, previously filtered through gauze, and boil in it. Unfortunately, it is impossible to give exact advice on how strong the decoction should be, because two outwardly identical plants may contain different amounts of coloring matter. So the concentration and processing time will have to be selected empirically. Let's name a few plants from which you can get good coloring decoctions for fabric. Let's start with the already mentioned onion peel. In its decoction, the fabric will turn yellow-red if etched with alum, and green if etched with iron sulphate. Onion peel has been used since ancient times for dyeing wool and linen. Potato leaves and stems can also be used to make dye. Their decoction will stain the fabric in a lemon color if the fabric is pre-treated with a solution of some kind of tin salt. And a decoction of the rhubarb root will give the tissue, etched with a solution of iron sulfate, a marsh color. For dyeing wool, decoctions from the bark of trees can also be used. So, alder bark will dye wool dark red, ash bark - blue. Wild pear wood contains a brown dye (wool must be etched in an aqueous solution of some bismuth salt before dyeing). There is a gray-green dye in birch leaves, however, it is not very effective. In the old days, it was rare, but still, they dyed the wool with a solution of coffee, only raw, to get a green color. Try this dye too, since you need very little raw coffee beans. They must be ground and boiled with the addition of washing soda, and the wool, before immersing it in the broth, pickle in a hot solution of alum. If this activity is to your liking, check for yourself the coloring effect of other plants in combination with different mordants. It is possible that you will find some unknown or completely forgotten combination, and the coloring will turn out to be extremely beautiful. Author: Olgin O.M.
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