Making molds out of clay

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    I would like to create my own mold designs for fairly small (5 inches wide or less) clay molds for glass slumping or draping. Has anyone done this? Is it possible to use low fire pottery clay and fire it in my Skutt Hot Start Pro glass kiln? Any help is appreciated.


    Works fine with low fire clay. Once you make the mold, fire it as high as your kiln will go.

    Remember to kiln wash it before firing with glass.


    Barry Kaiser

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    thomas decker

    I to am experimenting with making my own molds using low fire clay. my first attempt blew up in the kiln I am looking for advise as far as a fireing schedule  for clay in a glass kiln.  any suggestions?



    Two possible reasons for clay objects blowing up in the kiln:

    1) The clay was not completely dry. Clay must be absolutely dry before placing in the kiln. Objects of clay should be relatively thin: plate and tile molds can be 1/8″ thick. Always allow clay to dry for at least a few days before firing. If it feels cool to the touch, it’s probably still damp.

    2) Depending on the shape of the mold, there may have been hidden air pockets. Every clay tutorial will tell you that clay needs to be wedged before working it. Wedging clay is exactly like kneading dough. Clay needs to be wedged in order to push out the air pockets. Periodically cut through the clay using a wire cutter and check for air pockets.

    Another way to wedge clay is to repeatedly slam the clay onto a surface with some force; reposition the clay ball in your hands each time so that the clay ball remains ball shaped.


    thomas decker

    thanks  I just fired my second mold and it came out really well  so the blowing apart problem seem to be solved But I am still wondering about a firing schedule  the one I used seems to be excessively conservative and I am wondering if it really needs to be.  the pieces that I am making are about the size of a platter and about 3/8″thick the schedule used  was 80to 180 hold 3-4hr  150-500-hold10min  200-1000hld 10 – 300-1798 off  I know they say if it’s not broke don’t fix it , so  I quess that I am looking for some conformation that I am on the right path or did I just get lucky?



    I have fired some clay molds that were 1/8″ to 1/4″ thick and they work beautifully! I let them dry for several days to make sure there’s no moisture left and then fire them at R250 to 500, hold 0, R AFAP to 1800, hold 0 (off). This took about 4-1/2 hours. 3 coats of kiln wash and then I used my fire polish program to slump single thickness of glass. (These molds are less than 5″ dia.) Worked great!


    Your firing schedule is excessively conservative. I have made many molds from low fire clay and my schedule regardless of thickness follows….

    Dry 1-2 weeks with plastic over (prevents cracking)

    Dry on top of kiln overnight (during the firing of other items)

    To cure or complete the mold my kiln firing is………

    300 -1000 hold 30min

    500-1500 hold 5min

    off (let cool basically overnight)

    then wash with kiln wash like any other mold.

    Never had a problem and still use every mold I have made.




    Thanks for putting this on the forum. I always wanted to try to make my own molds and I never knew how to do it. I will definatly give it a try.

    Thanks again



    I do agree with Suzan K about the two possibilities for the blowing up of your mold.

    Conserning the firing of the low firing clay,I suggest you to verifiy with the maker of the clay.

    When I made my molds of low firing clay I used the code “cone”firing schedule.I have the option between glass or ceramic firing.Pottery (clay) is not as difficult to fire than glass.When I used cone firing,I had the option low,medium or fast firing.I used cone 08 (1750*F) .It went to room temperature to 1750*F. Than at 1750*F I shut down the kiln(at off).

    The next morning, the mold was fine and I still used them often.Sylvio


    I too would like to make molds for glass cabs out of polymer clay, can anyone suggest a brand of clay and will this method work for cabs if I need to add wire in the mold as part of the cab? Thanks.


    Good morning and hello ☺️

    I am new to this group and got here at the right time/right subject!

    Making molds for fusing has been on my (feeble) mind for past few weeks…..can high fire clay be used?

    I have about 10+ pounds of this stuff as I am in week 4 of a slab- hand building class.  I am hoping this clay can be repurposed for molds as it is not looking too good for the class projects!


    patsy monk

    choose to be healthier!


    I would not use polymer clay as it will burn at high temperatures used to fire glass.

    I used natural air-dry pottery clay I found at a craft store. It needs to be fired after air-drying for a few days (see comments above for firing temps). Then kiln wash it and give it a try!


    Lynn, which air dry pottery clay did you use?


    thomas decker

    any ceramics suply house will have a clay that is sutible  since you are not going to glaze it you dont really have to wory all that much about what kind of  clay just one that will bisque at a lower temp.  I use a white clay and only fire it to about 1400 .


    Good advice and information, thanks to all.
    Is it necessary or desired to put holes in the bottoms of the slump molds?
    I’ve read that it’s important, but have seen plenty of commercial molds that are smooth. 

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