Creating Flat Bottoms by Hand

No jokes please!

Often the moulds we use do not have a suitably flat bottom to them, making the resulting item wobble when set on a flat surface.  There are several ways to create a flat spot in the mould, reaching in to re-set the glass while firing, putting the glass in at a complimentary angle for a second firing - but they are not always successful.  

Of course, if you have the money you can use a flat lap or a linisher with a back plate to grind a flat spot on these bowls and other unstable pieces.

But,

You can still make a flat spot on your piece without machine tools.  Use a piece of float glass larger than your piece as your grinding base.  Put a slurry of 100 grit sand on the base and put your piece over.  Holding it level, make circular motions with firm downward pressure.  In only a few minutes you will have produced a large enough flat spot to stabilise your piece.

If you do not like the mess of the slurry, fasten a 100-grit sandpaper onto float glass, add water and do the same as you would with a slurry of grit.

An excellent video by HIS Glassworks comparing hand and machine coldworking is available here.