You probably have enamel stuck to the trivet, and every time you put a new piece in the kiln with that trivet the glass that's on it gets molten again and sticks to the new piece.  Next time you have the kiln running, take a bucket of cold water and place it nearby.  Put the trivet in the kiln and let it get red hot.  Take it out and dump it immediately into the cold water.  That usually cracks the glass off for me, but sometimes it needs an extra little tap with a hammer.  

Some people also coat the backs of their pieces with a kiln wash to keep them from sticking.

Or use alundum stone or diamond burr to clean the enamel from trivet.

R.

Thank you for all your replies. I have filed, used diamond burrs, placed water near by, used kiln wash to the trivet but not to the enamel pieces. Today I have turned down the heat to 800 degs C and left it till the piece is nice and shiny. But unfortunately they stick a bit. Maybe I need more than just one trivet, so the trivet can cool down before use again.

I think also it is a matter of trial and error to see what works best.

Can you a picture send to this forum, that one the trouble can see ? I suppose, that the mistake lies in supporting the piece to the trivet, or that you  an improper trivet use. Only the wings of the trivet should touch the outline of the piece. 

A problem could also be the steepness of the trivet-wings. If the trivet have steep wings, conter enamel touch the wings only in a very small area.
At flat wings, the contact area of the conter enamel is much larger.
To make clear what I mean, here two scetches.

Hi Edmund

Is there any specific trivet which would be best to use? How many trivets should I have? What kind? And where can I purchase them, Australia has a very limited supply?

Thanks

No. there is no universal-trivets.

A multifunctional trivet is the in the left picture shown trivet.   The little wings are not fixed and can be placed in every direction. It is not only for many flat, round or angular work pieces usable, but also for dishes or bowls if you fire this topside-down. 

If the standard-trivets, which one can buy by all enamel suppliers, are not suitable, you must construct the trivets by yourself. Normally one makes small trivets from 0,3 mm thick, larger trivets by 0,5 mm thick stainless steel. The form of the trivet is depending from the dimension and the form of the work piece. Important is, that the wings only touch the outer edges of the work piece.

You can also construct trivets from stainless steel wire or stainless steel nets.

Ceramic supplier sells also trivets from hard fired clay. The disadvantage of this is that it leaves marks on where they touch the enamel.

If the trivet-wings only touch the rim of a work piece the mark into the enamel are very small. You can remove it with a diamond milling tool or diamond wheel or with carborundum paper or carborundum stone-file.

More information how is trivets to make, you find in the file down on this page:

Production of trivets

Edmund

Hi Edmund 

Thank you for this information as it explains clearly. This has been most helpful and totally appreciated.

Thanks again.

Tony

Hi 

I am having troubles with copper items sticking to the trivets. How do I overcome this? 

Thanks 

Tony