Glass Working Exercises 93 



glass working. Any excitability or rashness, any attempt at 

 extraordinary rapidity will almost inevitably lead to failure, 

 though it is admittedly difficult for a beginner to restrain some 

 excitement at the instant the heated glass reaches the correct 

 condition for making an important joint. 



When an exercise is completed, it is usual to cool the 

 glass slowly. This is done by holding it in a flame of 

 gradually decreasing temperature (e.g. the luminous blowpipe 

 flame), and evenly distributing a coating of carbon over the 

 worked portion of the glass, gradually withdrawing the work 

 from the hot flame, and finally allowing it to stand for some 

 time before removing the carbon with a soft duster. This 

 gives the glass an opportunity of accommodating itself to any 

 undue strains, and to this end the temperature should, at first, be 

 as high and as fully and equally distributed over the worked 

 portion as possible, which should be just short of softening, in 

 fact. Gradual cooling will then, in most cases, prevent, or at least 

 minimize, subsequent fracture. A second and excellent method, 

 in case of complex glass work, is to wrap it up quickly in cotton 

 wool, which, of course, burns near the hot glass, but this does 

 not matter. This process of " annealing " is an important one, 

 especially for the beginner, who by its aid may frequently save 

 a piece of apparatus that would otherwise go to pieces on 

 cooling ; but it is noticed that the more expert a glass-blower 

 becomes, the less he makes use of the annealing process. The 

 reason appears to be that he equalizes all strains in the working 

 up of the glass, taking care to keep all the glass at as high a 

 temperature as possible until the work is completed, and also 

 paying special attention to the securing of an equal thickness 

 of material throughout. This latter point, indeed, is one 

 which is somewhat overlooked. Glass work perfectly stable 

 at high temperatures will crack on cooling, if different parts are 

 of different thicknesses, and although careful annealing may 

 preserve such a piece of work for the time being, in all pro- 

 bability it will snap under the slight difference of temperature 

 resulting from handling, even though three months have 

 elapsed since its manufacture. Such pieces of apparatus are 

 treacherous, and are sources of considerable inconvenience to 



