Cleaning of Glass Tubing:

Glass should be thoroughly cleaned before any glassblowing is attempted, since dust or foreign material may cause the glass to denitrify while it is being heated. In extreme case when the glass has not been properly cleaned, even the apparatus may crack after it is completed and cooled, even when it has been properly annealed. Merely running water through the tubing is not sufficient, as the water may not remove all the dirty residues. A wet rag should be forced though the tubing by means of a wooden stick. It is a good practice to avoid metal or glass rods  for this operation, since they may scratch the walls of the tube  being cleaned . The outside of the tube should also be rinsed with water and wiped with a damp cloth, and both  inside and outside wiped with a clean, dry cloth.

Care should be taken to keep finger marks from the glass since these marks readily burn into the glass and they are very hard to remove. Cleanliness of the hands is very important. 

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