Part 5 (1/1)

_Blowing a Bulb or Expanding a Join_--Prolonged heating is necessary in order that the thick partsshould take place by stages, in order that the thin parts, which tend to expand first, have time to cool The thick parts can then be expanded by further blowing and thus a bulb or expansion of even thickness can be obtained

_Cutting Glass_--The eneral use is by lass-blowers' knife Either file or knifeNeither file nor knife should be used on hot glass

The dialass, and when the dia noise is an indication of a satisfactory cut

_Leading a Crack_--A crack may be led in any desired direction by lass which it is desired to crack should be heated at a point slightly in advance of the crack, which will extend in the direction of the source of the heat

_Turning Out the End of a Tube_--This is done by heating the end of the tube and rotating it against an iron rod The rod must be kept polished and free from rust, and it must not be allowed to becolass will stick to it

_Joining Unlike Glasses_--Joints between unlike glasses are often unstable When such joints are made it is desirable to blow thelasses in any complex joint, such as an internal seal A transitional portion of tubing may be built up by the successive addition and interfusion of beads of one of the glasses to the end of a sealed tube consisting of the other glass

_Joining a Tube to a Very Thin Bulb_--The bulbon a bead of glass and expanding this slightly

A small central portion of the expanded partand the tube joined on

_Insertion of One Bulb Within Another_--A bulba crack round it and the inner bulb is then introduced The two halves of the outer bulb e to the edges), and the bulb es before the blowpipe until they are soft, and then expanding slightly by _--For most purposes, in the case of thin, blowpipe-lass apparatus, it is sufficient to cool slowly by rotating the finished article over a shts, and where the hot glass will not co

Si; but thick articles, and especially those that are to be subjected to the stress of grinding, needin a special oven

_Use of Lead-Glass_--When lead-glass is to be used, the blowpipe flalass should not be allowed to approach so near to the blue cone as to be blackened Slight blackening lass in the extrelass articles tend to be rather lass

_Combustion-Glass_--This en is introduced into the air hich the blowpipe flaen there is a risk of da the blowpipe jet, unless a special blowpipe is e these, one, in which the inner portion of the tube is fused on to the inside of the bulb or tube through which it is to pass, an opening isand the outer tube is joined on This is a quick and in some ways more satisfactory method than the other, in which there is no separate inner piece

_Rubber Blowing Tube_--In complicated work it is often convenient to use a thin rubber blowing-tube which is connected with the work either by a cork and piece of glass tubing or by fitting over a drawn-out end

The use of such a blowing-tube avoids the inconvenience of raising the work to the mouth when internal air-pressure is required One end of the rubber tube is retained in the lass-blowing is spoiled through carelessness in arranging the work beforehand The student should have every detail of his manipulation clearly in mind before he co thethe actual manipulation

Undue haste is another fruitful source of failure Practically every operation in glass-blowing can be carried out in a perfectly leisurely manner, and it is better to err rather on the side of deliberation than on the side of haste

If, as will doubtless happen at tiives trouble and it is necessary to pause and consider the whole question, or if for any other reason it is necessary to stop during the construction of a partially finished join or other operation, great care should be taken not to allow the work to cool A large, brush-like flaas admitted to the blowpipe, and the work should be held just in front of the current of hot air produced by such a flame

It will then be possible to continue work on this without causing it to crack when further heat is applied

As ti confidence in his ability toconfidence will coreatest obstacle to success in glass-blowing is undue haste in manipulation