Water on the brain

Casting the glass is one thing, getting it to look presentable is another.

The images below show how the glass came out of the plaster mould.  You can see how there are elements of the plaster that have bitten into the glass, some have stuck to the glass and all of them have left a mark; a textured layer that is not desired and that stops the glass sparkling.  The bottom picture also shows a shoulder of glass that is a remnant from the moulding pour process.  It requires a lot of cold work to get this glass to a finished state.

The glass shoulders were removed using a conventional glass grinder.  It has to be stressed that all of these cold working techniques use water to cool and lubricate the glass and the materials used to grind and polish. Remember, use water regularly!

After using the grinder I then used diamond coated hand pads to steadily and gradually grind and polish the surfaces.  The hand pads are graded based on the size and density of the diamonds imbedded on the pad.  You have to start off with the most coarse (60 grade) through to the finest (120, 200 and 400).  There are finer grades of pads however I don't have any.

The pads are dipped into a tub of water regularly and then rubbed onto the glass in a circular motion, being firm but not pushing too hard to ensure the glass isn't scored.  The next pad is rotated in the opposite direction as each pad is working to remove the ridges of the grooves created by the previous pad.

This is a good process to smooth off the surfaces however removing residue from the folds of the brain requires a different approach.  Soaking in vinegar or a release is useful to assist a stiff brushing from a nail brush or old toothbrush however this doesn't always remove all residue.  In this casting there was a lot of plaster that wasn't being removed.

I decided to use hydrofluoric acid to etch out the residue.  I didn't want to soak the cast in the acid so chose to apply it by brush.  This approach required me to use a much stronger percentage of acid so additional care had to be exercised.  This was very effective and didn't impact on the glossy finish that was in most grooves.

The end result is a big leap forward from its starting point

My next stage is to move onto a flatbed polisher to do two things; first to bring the upper surface to a glossy finish and the other is to grind the base to a flat finish so that I can use ultra violet bonding to affix the cast to its float glass carrier.