JONES, ON JAPANNING AND VARNISHING. 7 



tion. The species of gum most extensively used, is gum arable, 

 or Senegal ; that which exudes from plum, peach, and other trees, 

 possesses similar properties. Gum water may be considered as 

 the most simple of the varnishes ; it is sometimes used on pictures, 

 and on painted toys, to give them a gloss, but as it is readily dis- 

 solved by water, it is of little value ; sometimes it is employed be- 

 fore using spirit and oil varnishes, to prevent their sinking into the 

 substance varnished ; of this we shall speak more fully, when treat- 

 ing of varnishing upon paper. Some writers consider insolubility 

 in water, as an essential characteristic of varnishes, and do not 

 therefore view solutions of gum, as belonging to the number. 



Gum tragacanth, also called gum dragon, is sometimes used, as 

 will hereafter appear. This gum does not dissolve like the former, 

 but when covered with water, it swells and becomes a soft pulp, 

 which will mix with other mucilages, and dries hard and glossy, 

 but will not resist water. Most plants contain a considerable por- 

 tion of gum, and many a very large quantity. 



The resins, like the gums, exude from certain trees, either spon- 

 taneously, or from incisions made for the purpose. They resem- 

 ble the gums in external appearance, but differ from them essential- 

 ly, in many of their properties. The resins are softened and melt- 

 ed by heat, the}' burn freely, and with a vivid flame, and generally 

 with a fragrant smell. They are insoluble in water, but most of 

 them dissolve readily in alcohol, and, probably, they are all soluble 

 in this fluid, under proper precautions. The resins are precipi- 

 tated from their solutions in alcohol, by water, a small portion of 

 which, dropped into any spirit varnish, will immediately render it 

 turbid, or milky. This fact should be remembered, as it will be 

 found of importance in ihe process of varnishing. The resins are 

 generally soluble in ether, and in essential oils ; many varnishes 

 are made by dissolving resins, in oil of turpentine ; and other es- 

 sential oils are occasionally employed to promote the solution of 

 some of the most refractory of these substances. The fixed oils 

 dissolve many of the resins. Linseed oil, is the one most com- 

 monly used for this purpose, forming what is called an oil varnish. 

 Common rosin is the most familiar exam})le of the resins. Copal, 

 Mastich, Sanderac, and several others, are also in common use. 



There are some substances found in the earth, which strongly 

 resemble the resins in their general properties ; of these the most 

 important are amber and asphaltum ; both of which are used iit 

 varnishes, and will be again noticed in their proper places. 



The gum resins are principally used in medicine ; they are, as 

 their name indicates, mixtures of resins and gums, which exude to- 

 gether from the same tree. They are dissolved in common spirits, 

 which is a mixture of alcohol and water, the former dissolving the 

 resin, and the latter the gum ; they are generally turbid when dis- 

 solved, soft and brittle when dried, and partially acted on by wa- 

 ter ; and, being, therefore, uiifit to form the basis of varnishes, do 

 not require from us any further notice. 



Brilliancy, hardness, and toughness, are essential properties iit 

 varnish. These are posesssed in very dillerent degrees by the 



