Question:
How do I care for my molds?
Air bubbles
Air bubbles (pinholes) in greenware can come from air in the slip from stirring too briskly or pouring too rapidly.
Air bubbles on rims of pieces can be reduced by rocking the mold while pouring.
Dis-assembly
Before casting a multiple-piece mold, take it apart and examine it so you will know which piece should be removed first after the slip has been poured and the greenware is ready to be removed. To help you remember the disassembling order in a multiple-piece mold, use a waterproof marker to number the pieces. If there is something special that you must know about a particular before casting it, such as “drain with straw”, mark the outside of the mold with a waterproof marker. Once you have examined a new mold for any breakage and are ready to pour. Look it over one more time to see if it has any special problems you will have to cope with such as a small pour hole, undercuts, tricky draining etc.
Repair
It is possible to use condensed milk to glue the parts together if your broken mold if fairly small and the break clean, without too much chipping. Pieces must fit together smoothly to use this repair method.
It is possible to mend broken molds with glue but you must be careful not to get any glue on the mold. If any does spill onto the face of the casting area, be sure to remove it with fine sandpaper so the pores will not be clogged.
Drying
It is important not to dry your molds too fast. Store them on slated shelves so that the natural air can circulate around them.
When buying a new mold be sure you always open it immediately to inspect the inside for any damage.
When cleaning the inside of a mold, never use anything other than a brush. If you encounter a stubborn piece of clay simply roll some waste clay into a ball and pounce it off.
Since molds work on the principle of absorption, it is important that you avoid touching the inside with your fingers. You do not want to leave any oil residue that may clog pores.
Be sure that you remove all dried clay from the seam area of a mold. It can dry and when you put the mold back together and start pouring again, the dried clay may warp the mold and eventually cause rust spots on your molds.
You may notice a fuzz on your molds when they are being sorted. This fuzz is caused by deflocculents in the slip that have penetrated the mold. You should remove this fuzz as it will harden and plug the pores of the mold.
Sticking
If you have a new mold that sticks together and, no matter what you do, will not open, try saturating the seam area all around with water by pouring it right onto the mold. Then go ahead and cast it in your normal manner and it should open easily.
Handles.
When pouring cups, be sure to lie the mold with the handle down after draining so any excess slip will fill the handle and avoid leaving a bacteria trap.
Keep insect free
If you live in an area where bees, bugs, wasps etc might build a nest in your stored molds, be sure to cover the pour holes.
Stick ons.
Tiles or stick-ons which seem solid may blister or explode in the kiln.
Narrow stick-ons or small castings which are incomplete may be caused by too thick slip.
Greenware Sticking
To release greenware that sticks to a mold, use your air-brush
Drying
It can take many months for a large plaster mold to completely dry out, so it will continue to get lighter as that happens. But it is usable immediately. If using the same piece of plaster over and over, it will eventually become too wet to release the clay. Let it dry and it will again work fine. If you can't wait for the plaster to dry, you can sprinkle with talc.
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| Guru Spotlight |
| Lynne Christen |
