9 2 Laboratory Arts 



see Fig. 82. It may be taken for granted that most of the un- 

 evenness in glass work is due to unequal heating of the glass, 

 consequently the importance of this point can hardly be 

 overestimated. 



Much importance is also to be attached to the size of flame 

 used, and no hard and fast rule can be given here experience 

 is the best and practically the only guide. Too small a flame 

 localizes the heat unnecessarily, while too large a flame gives 

 an inconveniently large quantity of hot glass, which is apt to 

 get beyond control. At the same time, expert glass workers 

 can control larger quantities of hot glass than beginners can, 

 so make use of larger flames, and produce their work much 



V^ J UrtequaZty heated 



Dually heated 



FIG. 82. Showing effect of working glass when unequally heated, and when 

 equally heated, through incomplete and complete rotation respectively. 



more rapidly. As dexterity increases, larger flames may be 

 used, but it is recommended that small flames be used at first. 

 When removing hot glass from the flame for blowing, it should 

 be remembered that if blown immediately, the thin portions 

 will become thinner, but if allowed to cool for two or three 

 seconds before blowing, the thin portions will have hardened, 

 and therefore the thicker portions will become thinner. Con- 

 trol may therefore be exercised in this way. 



All work in glass blowing should be done calmly and 

 easily. A slow motion of the foot, gentle handling of the 

 glass, quiet and easy movements of the various portions of 

 apparatus under construction are the characteristics of expert 



