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FLASKING, VULCANIZING AND FINISHING. 55

thickness of the mass, as i/ic licat if riiii up too rapidly zvill
cause the rubber to become spongy or porous.
When the vnlcanizing" point is reached the flame should
be sHghtly lowered, so that the temperature will remain
uniform throughout the operation. The time required to

Fig. 27.

effect vulcanization is usually one hour from the time the
heat reaches the vulcanising point. When this time has
expired, cut off the flame and allow the vulcanizer to cool
to at least 200, when, if necessary, it can be hastened by
placing it in cold water. Certain advantages are obtained
by allowing the cooled flask after the vulcanization to
remain unopened for at least several hours. It is claimed
that a molecular accommodation of an annealing character
thus occurs, with a consequent diminution of liability to
warp the plate or break the porcelain section. The long-
continued retention of the denture on the model within the