43« 



MECHANICAL. 



tharge, one part ; spirits of turpentine, one 

 hundred and seventy parts. Pursue the 

 same treatment as before, and mix the 

 two varnishes while hot. 



VARNISH, Crystal — Picked mastic, 

 four ounces ; rectified spirit, a pint ; ani- 

 mal charcoal, one ounce. Digest and 

 filter. 



VARNISH FOR CHROMOS. —The 

 best varnish tor chromos is made of gum 

 mastic dissolved in spirits of turpentine. 

 It should be of such thickness as to 

 spread easily and evenly with a common 

 varnishing brush. If a chromo is not 

 oil-colors, two coats of size (isinglass 

 dissolved in water) should be first given 

 to it. When the size is dry the varnish 

 may be laid on. Two or three coats may 

 be needed to get a good surface, which 

 should be perfectly free from cracks. 

 This varnish may be cleaned with a soft 

 sponge and soap and water. It is equally 

 serviceable for maps and drawings as for 

 chromos or paintings. 



VARNISH, Copal, to dissolve in Alco- 

 hol. — Copal, which is called gum copal, 

 but which is not strictly either a gum or 

 a resin, is the hardest and least change- 

 able of all substances adapted to form var- 

 nishes, by their dissolution in spirit, or 

 essentials, or fat oils. It therefore forms the 

 most valuable varnishes; though we shall 

 give several receipts where it is not 

 employed, which form cheaper varnishes, 

 sufficiently good for many purposes, 

 adding only the general rule, that no 

 varnish must be expected to be 

 harder than the substance from which it 

 is made. 



To dissolve copal in alcohol, dissolve 

 half an ounce of camphor in a pint of 

 alcohol; put it into a circulating glass, and 

 add four ounces of copal in small pieces ; 

 set it in a sand-heat, so regulated that 

 the bubbles may be counted as they 

 rise from the bottom, and continue the 

 same heat till the solution is completed. 



The process above mentioned will dis- 

 solve more copal than the menstruum 

 will retain when cold. The most economi- 

 cal method will therefore be to set the 

 vessel which contains the solution by for 

 a few days, and when it is perfectly set- 

 tied, pour off the clear varnish and leave 

 the residue for future operation. 



The solution of copal thus obtained is 

 very bright. It is an excellent varnish 



for pictures, and would doubtless be an 

 improvement in japanning, where the 

 stoves used for drying the varnished 

 articles would drive off the camphor and 

 leave the copal clear and colorless in the 

 work. 



VARNISH, Copal, to Dissolve in 

 Spirits of Turpentine. — Reduce two 

 dunces of copal to small pieces and put 

 them into a proper vessel. Mix a pint of 

 the best spirits of turpentine with one- 

 eighth of spirits of sal ammoniac; shake 

 them well together, put them to the 

 copal, cork the glass and tie it over with 

 a string of wire, making a small hole 

 through the cork. Set the glass in a 

 sand-heat so regulated as to make the 

 contents boil as quickly as possible, but 

 so gently that the bubbles may be counted 

 as they rise from the bottom. The same 

 heat must be kept up exactly till the solu- 

 tion is complete. 



It requires the most accurate attention 

 to succeed in this operation. After the 

 spirits are mixed they should be put to 

 the copal and the necessary degree of 

 heat be given as soon as possible, and 

 maintained with the utmost regularity. 

 If the heat abates or the spirits boil 

 quicker than is directed, the solution 

 will immediately stop, and it will after- 

 ward be in vain to proceed with the same 

 materials; but if properly managed, the 

 spirit of sal ammoniac will be seen grad- 

 ually to descend from the mixture and 

 attack the copal, which swells and dis- 

 solves, excepting a very small quantity 

 which remains undissolved. 



It is of much consequence that the 

 vessel should not be opened till some time 

 after it has been perfectly cold, for if it 

 contain the least warmth when opened 

 the whole contents will be blown out of 

 the vessel. 



Whatever quantity is to be dissolved 

 should be put into a glass vessel] capable 

 at least of containing four times as much, 

 and it should be high in proportion to its 

 width. 



This varnish is of a deep rich color 

 when viewed in the bottle, but seems to 

 give no color to the pictures upon which 

 it is laid. If it be left in the damp it 

 remains racky, as it is called, a long time; 

 but if kept in a warm room or placed in 

 the sun it dries as well as and other tur- 

 pentine varnish, and when dried, appears 



