Suppose a glass shade to be cracked at the bottom for about 1/2 in. up, and that it is desired to cut off the cracked portion without breaking the top part of the shade. First make an ink mark round the shade a little below the end of the crack. Now obtain a tube with a fine jet - a mouth blowpipe will do, or a glass tube drawn to a fine point, or even the mouthpiece of a clay pipe. Connect this to a piece of rubber tube and thus to a gas bracket. Now light the gas, keeping the flame as small as possible. Lay the shade on a table with the crack uppermost and place the flame between the crack and the ink mark; hold it there a moment, then raise it, and as the crack moves along, keep touching the glass carefully with the flame and lead the crack completely round the ink mark. At the end of about five minutes it will be possible to remove the cracked portion. To finish, carefully touch up the sharp edges of the shade with a piece of emery paper.