Gathering for Feet
From the glass makers point of view, you want the foot gather to be ready and above your vessel or stem; hot, round and presented well enough to fall off efficiently.
The iron temperature is an important factor. Too hot and you will gather less and increase the chance of bubbles forming from the iron its self. Too cold and although it may look like a big gather not much of it falls off. This is because the cold iron has drawn the majority of the heat from the glass. See the picture above for a cold iron gather. You can see the way its pointed up after its fallen. That’s a sign that the iron is cold and has made the surrounding glass cold enough to hold onto the bulk of the gather.
The position of the glass in relation to the iron is extremely important. If all of the glass is on the iron; when if falls it will fall in an oval shape and will also cause temperature imbalances all over the gather. If the glass is too far off the iron it will cool faster as it gets thinner and longer. As always with glass the trick is getting it in between two variables.
A good glass maker can still make the foot but a good gatherer will make a better glass maker.