Home Forums Explore Media Clay Please Help!!! Removing A Large Bowl From Casting Mold

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  • #988456
    cd_riggs
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        I am wondering if someone could please help with removing a 16in x 5in bowl from a slip casting mold? I have tried several times and I always end up ruining the bowl in the process. It gets stuck on there and you can not get it off. I have done slip casting before and have never had problems with anything but the bowls they seem to suction down. Is there a step I am missing with the bowls in order to get them off?

        Thanks for the Help
        Dawn

        #1135874
        Rob Hendriks
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            Some general tips;Keep in mind that earthenware clay is easier to cast then stoneware or porcelain slip.The mold has to be dry, and have no undercuts, or a too difficult form for casting.

            The slip must be not to thin when pouring, and must stay for 10min.-20 min. in the mold,otherwise the bowl becomes to thin.

            Using a rubber hammer can be a help to loosen the model from the mold.Adding a bit ball clay can make the slip more plastic, and ease loosening from the mold.

            #1135878
            SarahMgee
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                I have seen some people use an air compressor to blow a bit of air between the mold and the bowl to loosen it as it comes out. This is done after the clay has reached the leather hard stage – but I have not done this myself.

                #1135879
                cd_riggs
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                    Thank you Rob and SaraMgee for your help. I will be pouring a new one today here in a little while. I will be trying all of your suggestions. Once again thank you

                    Dawn

                    #1135875

                    I’ve heard of the using the air compressor as well. My understanding is that the air can be applied to plaster mold itself as plaster has tiny holes throughout it. So the air pressure will go through the mold and help to loosen the clay cast. Please let us know how things go and what works. :thumbsup:

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                    #1135876
                    saje
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                        a couple potentials
                        what/where of the mold: did you buy or make the mold? what plaster/water ratio was used to make the mold? was the plaster a casting plaster? is the clay sticking to the mold? is there an undercut in the mold, as, is the clay shrinking from the mold but still is hitting or catching somewhere?

                        if you use air to blow out the clay from the mold it must be a very low pressure. if the air is to strong it will blowout the clay or/and possibly create a dry/dryer spot at the air vent which can cause a crack upon firing.

                        what is the moisture percentage of the clay? if it is suspect and you don’t monitor the fluidity, try dropping the moisture percentage. what chemicals do you use to control the fluidity of the slip? if you keep using water to increase the fluidity of the slip you will make the slip fragile, wet and such??

                        #1135877
                        saje
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                            also, are you drying the mold between casts or at least every couple casts. how long are you letting the cast piece in the mold? if you made the mold, how was the initial drying accomplished? i don’t want to ask too many questions but they are all necessary.
                            since this is my first post in “clay”, 25 years in ceramic manfacturing from bone china to earthenware, thanks

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