MEMBRANE, SINEW, HORN.
Parchment.--The substance which is called parchment when made from sheep or goat skins, and vellum when from those of calves, kids, or dead-born lambs, can also be made from any other skin. The raw hide is buried for one or two days, till the hair comes off easily; then it is taken out and well scraped. Next a skewer is run in and out along each of its four sides, and strings being made fast to these skewers, the skin is very tightly stretched; it is carefully scraped over as it lies on the stretch, by which means the water is squeezed out; then it is rubbed with rough stones, as pumice or sandstone, after which it is allowed to dry, the strings by which the skewers are secured being tightened from time to time. If this parchment be used for writing, it will be found rather greasy, but washing it will oxgall will probably remedy this fault. (See "Ox-gall," p. 331.) In the regular preparation of parchment, the skin is soaked for a short time in a lime-pit before taking off the hairs, to get rid of the grease.
Catgut.--Steep the intestines of any animal in water for a day, peel off the outer membrane, then burn the gut inside out, which is easily to be done by turning a very short piece of it inside out, just as you would turn up the cuff of your sleeve; then, catching hold of the turned-up cuff, dip the whole into a bucket, and scoop up a little water between the cuff and the rest of the gut.
The weight of this water will do what is wanted: it will bear down an additional length of previously unturned gut; and thus, by a few successive dippings, the entire length of any amount of intestine, however narrow it may be, can be turned inside out in a minute or two. Having turned the intestine inside out, scrape off the whole of its inner soft parts; what remains is a fine transparent tube, which, being twisted up tightly and stretched to dry, forms catgut.
Membrane Thread.--Steep the intestines of any animal in water for a day; then peel off the outer membrane, which will come off in long strips; these should be twisted up between the hands, and hung out to dry; they form excellent threads for sewing skins together, or indeed for any other purpose.
Sinews for Thread.--Any sinews will do for making thread if the fibres admit of being twisted or plaited together into pieces of sufficient length. The sinews lying alongside the backbone are the most convenient, on account of the length of their fibres. After the sinew is dried straight strips are torn off it of the proper size; they are wetted, and scraped into evenness by being drawn through the mouth and teeth; then, by one or two rubs between the hand and the thigh, they become twisted and their fibres are retained together. A piece of dried sinew is usually kept in reserve for making thread or string.
Glue is made by boiling down hides, or even tendons, hoofs, and horns, for a long time, taking care that they are not charred; then drawing off the fluid and letting it set.
Isinglass is made readily by steeping the stomach and intestines of fish in cold water, and then gently boiling them into a jelly: this is spread into sheets and allowed to dry. The air-bladder of the sturgeon makes the true isinglass. (See "Paste and Gum," p. 332.)
Horn, Tortoiseshell, and Whalebone.--Horn is so easily worked into shape that travellers, especially in pastoral countries, should be acquainted with its properties. By boiling, or exposing it to heat in hot sand, it is made quite soft, and can be moulded into whatever shape you will. Not only this, but it can also be welded by heating and pressing two edges together, which, however, must be quite clean and free from grease, even the touch of the hand taints them. Sheets of horn are a well-known substitute for glass, and are made as follows:--The horn is left to soak for a fortnight in a pond; then it is well washed, to separate the pith; next it is sawn lengthwise, and boiled till it can be easily split into sheets with a chisel; which sheets are again boiled, then scraped to a uniform thickness, and set into shape to dry. Tortoiseshell and whalebone can be softened and worked in the same way.