How big can a square be for a drape former?
The diagonal of the square for a former can not be more than twice the height of the former plus the base diameter. Of course it is better to be slightly smaller to allow for the glass stretching during the drape. But twice the height plus the base diameter is the maximum.
An example. If the former base is 2 and the height is 7, the diagonal can be no longer than 16 (7+7+2). The question then is what size square will that diagonal produce. The geometry formula of the sum of the squares of the two right angle sides equal the square of the hypotenuse (diagonal). That means the square pieces of glass cannot be more than 11.3. This is arrived at by:
Calculate the square of the diagonal (16*16) = 256
Divide that in two; half of the square is 128 (the square of one side)
The square root of 128 is 11.31
So the sides of the square are 11.3 each.
This is the largest square you can put on on that vase drop mould, because that size square has a 16 diagonal.
Or if you don't like maths:
Mark a line at a 45 degree angle from the corner of a piece of paper.
Mark off the length of the diagonal needed for the former on it.
Draw a right angle from the edge of the paper to the point that is the length of the diagonal. That is a measure of the sides of the square.
This will require some drawing tools.
A no-tools method:
Fold a piece of paper at the corner until the edges meet.
Crease the fold to give a 45 degree angle
Mark the diagonal length along that 45 degree crease
Fold the paper from the top toward the bottom where the 45 degree crease began.
When the mark for the diagonal is reached, carefully crease the paper to the edge.
That gives you the length of the size of square needed.
Circle sizes are a easier, because twice the height plus the base equals the diameter of the circle. So in the example above, 7+7+2 = 16 which is the largest diameter that can be used for that former.
