Next to glue, paste is the most extensively used, and the most valuable cement that we have. For ordinary purposes it consists simply of flour, made into a thin cream with water, and boiled. .It then forms a stifiisn mass, which may be diluted with water so as to bring it to any required condition of thickness. There are two distinct elements in flour, both of which are valuable, one is starch, and the other is gluten. The cheaper kinds of flour, and especially rye flour, are rich in gluten, while wheat flour is rich in starch. In the latter case, it is sometimes of advantage to add a little com-mon glue to the paste. For ordinary purposes no additions are necessary, but where paste is to be kept for a long time, various ingredients may be added, to prevent souring and moulding. A few cloves form, perhaps, the best preservative for small quantities. On the larger scale carbolic acid may be used. If it were not for the expense, salicylic acid would form a good preservative. According to the statement of Lunge, souring and moulding may be entirely prevented by the addition and thorough mixture with the freshly-prepared paste of a few gr. of salicylic acid.
When thus treated, a paste may be kept for weeks in a heated room without losing its freshness, and even when it has, by long standing, become dry and tough, may be at once rendered fluid and serviceable by treatment with hot water. The addition of the acid does not, according to this author, affect the stickiness of the paste to any sensible degree. When it is desired to prevent the attacks of insects, either before or after use, the addition of corrosive sublimate is a sure preservative, but as this substance is a powerful poison, great care must be exercised when it is employed. The following formulas give good results: -
(1) Starch Paste
This is best prepared by triturating the starch with cold water in a mortar until no lumps remain, and not too thick a mass is formed, and pouring into this boiling water very slowly, with rapid stirring, until the paste begins to form, as indicated by the increase of transparency, and then rapidly adding the rest of the boiling water necessary for the paste. Boiling the paste is very injurious, rendering it less adhesive, and liable to peel off. Rye flour affords a more adhesive paste than starch, but of a grey colour. The addition of a little alum to the water with which paste is prepared renders it more permanent, and the use of boiling lime-water instead of pure water adds to its adhesiveness. An aqueous extract of decomposed gluten, however, affords the best paste with starch. By incorporating with the paste a quantity of turpentine, equal in weight to half of the starch employed, and stirring well while the paste is still hot, it will be rendered more impervious to moisture, and at the same time more adhesive.
(2) Corn Starch Paste
Corn starch makes a good paste for scrap-books. Dissolve a small quantity in cold water, then cook it thoroughly. Be careful and not get it too thick. When cold it should be thin enough to apply with a brush. It is not so liable to mould and stain the paper as paste made from other kinds of starch.
Mix thoroughly 630 gr. of the finest Bermuda arrowroot with 375 gr. of cold water in a capsule, with a spoon or brush; then add 10 1/2 oz. of water and 60 gr. of gelatine in fine shreds. Boil, with stirring, for 5 minutes, or until the liquid becomes clear, and when cold stir in well 375 gr. of alcohol, and 5 or 6 drops of pure carbolic acid. Keep in well-closed vessels, and, before using it, work up a portion with a brush in a dish.
(4) 4 parts, by weight, of glue are allowed to soften in 15 parts cold water for some hours, and then moderately heated till the solution becomes quite clear; 65 parts boiling water are now added with stirring. In another vessel, 30 parts starch paste are stirred up with 20 of cold water, so that a thin milky fluid is obtained without lumps.
Into this the boiling glue solution is poured, with constant stirring, and the whole is kept at the boiling temperature. After cooling, 10 drops of carbolic acid are added to the paste. This paste is of extraordinary adhesive power, and may be used for leather, paper, or cardboard with great success. It must be preserved in closed bottles to prevent evaporation of the water, and will, in this way, keep good for years.
(5) Fine wheat starch, 1 oz.; beat into a paste with cold water; best glue, 4 oz. Soak the glue, and when soft, boil it and add the starch paste, stirring well. Boil the whole until it is quite thick, and set aside to cool. It keeps well, and when required for use may be instantly dissolved in a little warm water.
(6) 2 oz. starch, 1 oz. white glue, 1/2 oz. acetic acid, a few drops of oil of cloves. Dissolve the glue in cold water and then boil. Mix the starch with cold water, and pour into the glue while boiling.
(7) Rice flour makes an excellent paste for fine paper work.
(8) Gum tragacanth and water make an ever-ready paste. A few drops of any kind of acid should be added to the water before putting in the gum, to prevent fermentation. This paste will not give that semi-transparent look to thin paper, that gum arabic sometimes gives, when used for mucilage.
(9) Paste That Will Not Sour
Dissolve 4 teaspoonfuls of alum in 1 gal. water; when cold, stir in as much flour as will give it the consistency of thick cream, beat smooth, add 1 teaspoonful of pulverized rosin, and 20 drops oil of cloves, pour the whole into 2 qt. boiling water, stirring thoroughly until it is cooked; pour into a glazed earthen vessel, and when cold cover the top with oiled silk, and put it in a cool place; when needed for use, take out a portion and soften with warm water. This will be found very convenient for use at times when very little paste is required at once.
(10) Paste For Paper-Hanging
Take 1/2 quartern of flour (best biscuit) and put it into a pail, with a small portion of alum, broken up small; mix it up into a stiff batter with warm water; have ready a large saucepan of boiling water, and .pour it over the paste, stirring well all the time, or it will be " lumpy." If properly done, it will thicken as the boiling water is poured over it; if it does not thicken, set it over the fire a few minutes, but be sure you stir it, or it will burn. When well thickened, throw a dash of cold water over it, as it prevents it skinning whilst cooling. Use rather thin. You can thin it with cold water.
(11) Trimmers' Paste
Trimmers' paste requires to be smooth, elastic, as free from moisture as possible, and possessed of great adhesive qualities. If too moist, it will soil the cloth or silk to which it is applied, and if not well cooked it will mould and rot; its adhesive qualities are dependent upon the materials of which it is made, and the manner of mixing and cooking. The materials used are wheat and rye flour. The paste of commerce is made of a very low grade of wheat flour, cooked by steam; it is not a good article for trimmers, as it contains too much surplus moisture. To make wheat paste, select a low grade, but sweet wheat flour, and stir it into cold water until thoroughly dissolved; then place the kettle over a quick fire and stir until it boils; it should be allowed to cook 5 or 6 minutes after it is brought to a boil, and be well stirred while boiling and until it is cool; if made in this way, it will contain no surplus moisture, and will be smooth and free from lumps. For rye paste, select good fine rye. flour, place the necessary amount of water in a kettle over a quick fire, and when the water boils pour in the flour slowly, stirring it thoroughly; continue to add flour until the desired thickness is obtained; then allow it to boil about 5 minutes, after which remove it from the fire and continue to stir until boiling ceases, then cover and allow it to stand until it is cold.
Rye flour paste made in this way is the smoothest, most adhesive and elastic paste in use. It is particularly valuable for pasting cloth on wood or leather. The dry paste that gathers on the kettle should not be thrown away; if it is soaked in cold water until it becomes soft, and again heated up to boiling heat, it is stronger and more elastic than when first made. Wheat or rye paste can be preserved from mould, etc, by adding a little carbolic acid or essential oil. The addition of a little dissolved gum arabic adds materially to the adhesive qualities of flour paste. Paste for summer use that will keep a long time is made of rye paste, prepared as above: when cold, pour it on a smooth board and set it in the sun to dry; when dry it can be broken up and saved for use. To prepare it for use, place a small quantity in a kettle and cover it with cold water; allow it to remain until soaked soft, then pour off the surplus water, place the kettle over a quick fire, and stir it until it boils. Another plan is to cook the paste, pour it on a cloth, lay it in a clean, warm place for 10 or 12 hours, roll up the cloth, and lay aside for use.
Paste treated in this way will keep sweet for a week or more, even in the hottest weather.
(12) From Vanderdecken's Yarns for Green Hands: - " Next, you will require a good paste that will neither decay nor become mouldy; therefore, mix good clean flour with cold water into a paste well blended together, then add boiling water, stirring well up until it is of a consistency that can be easily and smoothly spread with a brush; add to this a spoonful or two of brown sugar, a little corrosive sublimate, and about half a dozen drops of oil of lavender, and you will have a paste fit to fasten the teeth in a saw." We may add that the paste is none the worse for being a day or two old.
Peasley - A recipe for this cement was published in a well-known technological journal about the time of the first appearance of the cement. Phin doubts the accuracy of the formula, however, and believes that the Peasley cement was merely a modification of the well-known Armenian cement, which see. The following is the recipe alluded to: Prepare a solution of 200 parts of white glue in water; another of 50 parts isinglass, 3 of gum arabic, and 3 of tragacanth; and finally, another of 1 part shellac in alcohol. Then pour these 3 solutions together, mix them with 24 parts of white lead, and add 12 of the best glycerine, and 200 of alcohol. The mastic thus obtained should be immediately put up in bottles and well corked.