Deep Bowl Schedules

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    I’m looking for advice/schedules for firing deep drops for 2 or 3 layers.

    I have a couple of molds that are around 13-14" wide and between 5-6" deep. 

    I have no troubles fusing the circles for the bowls, however my slumping schedule/temps are not working.  My pieces either do not slump evenly, or I lose one edge into the mold.



    Your best bet is to go very slowly (50 degrees an hour or so) starting at about 1050°F and creep up to about 1225°F.

    You should also make sure your kiln/shelf/mold are level.

    Even when you do everything right, deep slumps often drop catawampus.  Very often the piece can be repositioned in the mold and slumped a second time.

    One more option is to make your bowl blank bigger than needed and put a drop ring above the mold — then cut the rim after slumping.  That’s how I did the bowl in this forum thread here.

    Helios Kiln Glass Studio



    Deep slumps also require A LOT of babysitting to get it right. But yah – so far our best results have come with the way Paul described above. I’d love to hear if anyone else has had any other experiences! 


    ~ KPT



    Paul, when you refer to ” (50 degrees an hour or so) starting at about 1050°F and creep up to about 1225°F” are you saying to ramp at full speed to 1050, then creeping up at 50 degrees an hour to 1225?  Would you be willing to share your entire slumping schedule for this?  I’ve actually had the glass break in the middle before it had a chance to melt.



    Stephen Richard

    You have fused a piece of glass that is now 6 or maybe even 9 mm thick, so you have to go slow for two reasons at least. 1. you have to give the glass the opportunity to get hot all the way through.  2. fast temperature rises lead to breakages either on the way up or during the slump.

    So a rise of ca. 100 C or 150 C is as fast as you want to go.  When using slow temperature rises you often can achieve the work at a lower temperature, and with a longer soak are certain to get the work done.  Unless the glass is all of one colour/sheet all across itself, fast heating will lead to the darker and softer (not the same) becoming plastic before the rest of the sheet and even before the bottom is soft enough to begin to slump.  That is when the weight of the glass above can split the bottom without completely breaking the piece.

    Stephen Richard

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