How to Avoid Fusing Glass Stuck to Mold - Go Fusing Blog
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How to Avoid Fusing Glass Stuck to Mold

How to Avoid Fusing Glass Stuck to Mold


When firing glass in a kiln, it is very important to properly prepare your molds or the glass can fracture or become permanently attached to the mold so you will look your glass a working mold!

But if you do not do your proper preparations, do not despair, there still be a few things you can try to release the mold from the glass.

What Went Wrong and my glass is stuck to my mold?: As in the picture above, the glass has draped over the mold as was planned but it did not release when the glass had cooled down to room temperature.

Answer: All molds require a few things to be properly prepared for use in the kiln.

1. A good kiln wash should be applied to the mold in multiple thin layers and allowed to dry completely in-between. If you apply it to thick you will see brush strokes.

2. When you apply the kiln wash, it is very important that you make sure you clean out the holes in the mold regardless if the glass will end up covering the holes. The holes are there to allow air to escape from under the mold and/or glass and equalize the temperature and pressure inside and outside the mold. If the mold you chose does not have any holes in it, then you may have either purchased a defective one or it was designed for ceramic use and not glass slumping.

  • Clean out the holes using a tooth pick before slumping your glass.
  • Not all kiln wash brands are of equal quality so ask around and find out what others recommend. We recommend our Hotline Primo Primer

3. You can use our Thin Fire Paper draped over your mold instead of or in addition to Kiln Wash on your mold. But, Thin Fire paper can leave crease lines in you glass as the glass slumps over it and if you are going to use it, you need to make sure you cut it a least an inch larger all the way around the current size of the glass before your fire it in the kiln.

Solution: If you do find yourself with glass stuck on a mold you can try the following:

  • Allow the glass and mold to anneal back to room temperature.
  • Turn the glass upside down with the mold facing up or lay it on its side in the kiln on thin fire paper or a treated, kiln washed shelf. Then slowly fire the kiln up to about 1,200 degrees.
  • Once the kiln is over 1,000 degree it is safe to open the lid for a short period of time without shocking and cracking the glass. But, you must be prepared with your gloves and either a long pare of stainless steel tongs or tweezers so you can act quickly.
  • Put on your gloves and grab your tool(s). You made need one to push and the other to pull. Then open the lid at 1,200 and you should be able to separate the mold from the glass with a slight pull or push. If you were lucky enough to have use thin fire and kiln wash this should be easy. If you did not use thin fire and not enough kiln wash on the mold, this may take more than one try.

    The key is to not let the kiln get below 1,000 degrees and not much higher than 1,250 to 1,300 as you do not want the glass to start to move and perhaps make matters worse.
  • Once the two are separated. Close the lid and turn off the kiln and allow it to anneal back to room temperature.

We also recommend you read thru the Free Glass Tips and Tricks section of our website.