A Thermoplastic is a polymer that becomes pliable or mouldable above a specific temperature, and returns to a solid state upon cooling. Because of their molecular structure, most thermoplastics can be remoulded. A tough, engineering strength thermoplastic has recently found its way onto the marketplace, introducing some very interesting possibilities to the jeweller’s workshop.
Many of our members have begun to use such plastics (with brand names including Thermo-Loc and Polymorph) in place of setting wax, pitch and shellac. It can be heated with hot water or a hairdryer and moulded by hand, as well as being cleaner, quicker and completely reusable. Guild member Dave Wallis has kindly produced an introductory guide to thermoplastics for the jeweller.
It's fab, and really easy to use - fill a pyrex jug 2/3 full of hot tap water and top up from just boiled kettle = 65 deg C
Throw the granules in and squish a bit
The granules don't mix with water at all
Squeezing the frogspawn together after fishing it out gives easily worked lump
Mould around a setting handle or dopping stick and wait 15 minutes for the plastic to set - job done and much easier than expected!
Time to really put this stuff through its paces!
This is an old cast sterling setting - with a wall thickness of much less than 1mm it definitely needs setting in some sort of setters compound - the ideal test piece. It's also a bit too small for the stone, so I can expect to be giving it a lot of pushing - again a good test to see if it stays gripped!
I used a hairdrier to soften the end, which is a bit broad as it just softens it all over. I need something a bit more precise - maybe hot air gun.
In the meantime went with it and placed the sterling setting on the end and gave it a bit more heat with the hairdrier, the silver conducted the heat to where I wanted it! I should have thought of that earlier.
I used the wrong end of the tweezers to mound the polymorph around the setting, leaving the bit I'll be pushing over the stone clear, and pushing down inside the setting to create a well for the pavillion of the stone. Rock solid! It just needs putting to one side to set hard.
This setting is a bit small for the stone so takes a lot of 'adjusting' and I use a scraper to open it out so that the stone lies girdle level with the surface, this has been the point where the setting and the shellac used to part comany, due to the sideways force exerted by both scraper and pusher on the setting.
I've used scraper to remove metal, pusher to adjust the width to the stone and a flat and a lozenge (or star) graver to refine the inside of the setting ready for cutting the seat for the girdle. I also used a wide flat to remove more polymorph material from inside the setting to give me more depth to work in. It hasn't budged at all, and is still secure ready for the next op.
With shellac, the pushing and mucking about can cause it to pop out, requiring re-heating and reseating the setting on the stick, this is much better.
The stone now sits well in the setting.
I reheated it a bit and popped it out, any stuck bits peeled off easily (even from inside little nooks and corners) as it hardens a little.
The polymorph came through with flying colours, stayed solid and picked out clean after heating the piece to release it - no problems at all!