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longmountainart

How To Choose The Right Mould Material

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I have a few ceramic plants that take me a really long time to make individually and i would love to be able to cast them however, i am not sure how to decide whether i should use plaster or something softer like latex. Ive only ever used plaster but never on a form this intricate before. Its more like a high relief. I am thinking i would need to make a 3 part mould if i was using plaster but that is a bit scary since my individual leaves are delicate. Maybe i should bisque first? Help! TYIA Brittaini

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oldlady    1,323

welcome to the forum.  a photo of your work would be great to see.

 

i work with leaves a lot but i work with slabs mostly.  just tried making a circular planter from a slab of ginko leaves.  it works but is a little rough since it is a prototype.  this is it when still greenware and shows the poorly placed rim design.  this will be broken up since it is not good enough to keep but got the slab into round and a thrown bottom.

post-2431-0-75990600-1487786296_thumb.jpg

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Chris Campbell    1,088

An image would be good so we could see exactly what you mean ... I am imagining you are talking about a sprig type mold ... Put the clay in to make the item, then pull it out?

 

Liquid latex makes a strong flexible mold. Coat your prototype item with as many coats as you like letting each coat dry before applying the next. Latex is also forgiving enough the you can get away with small undercuts. When it is dry you simply pull out the original form and you are ready to go. I have had some of these for 10-15 years and they are still usable. You can also coat real petals with the latex to get even better patterns. I have done this with leaves, bark, moss etc. Make a depression in a clay slab, lay the petal flat in it then start applying the latex until it is thick enough.

 

You can also make flat press molds out of clay. Roll a slab to the size you want and impress it will all the shapes you want. Dry and bisque fire it.

Remember shrinkage and make the shapes a % bigger than you need.

 

I have always wanted to get a hold of the mold material my dentist uses for making crowns since it does not shrink when dry. I suspect it is expensive.

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oldlady    1,323

chris, ask your dentist for the out of date stuff.  i got some last year and it is great!  you need to have the applicator from him/her, though.  just ask, they will think it special to have an artist ask.

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The dentist stuff is called Algitec. They make 2 grades, one for the dentist that isn't stinky, and stuff that isn't for the dentist that reeks to high heaven. I never thought to ask the dentist for any. Good idea!

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oldlady    1,323

how are you making the individual petals?  if you are hand making each one, you can speed that step up by making a flat mold from raku clay or something like it.  each petal can be rolled into the slab from your original or from an actual leaf or petal if they are sturdy enough.  that way, you simply remove each one from the slab and insert it in place.  i can see that as a production step, the outer leaves first to peel off and working through to the smaller center ones. the double ended rubber sculpture tools would do this well. 

 

a raku slab can work well, if you try it, aim for a 3/8 inch slab so it will stay flat and not be liable to crack like a thicker one might.  when fired to bisque, support it on a piece of foam rubber or carpet pad so you can roll out each leaf or petal without putting a strain on the slab mold.  a pony roller works well, especially the one that is tapered.

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oldlady    1,323

you appear to be in some place with a british influence.  if you have ever seen wedgewood pottery, the blue background with the white figures on top, those white things are called sprigs.  sprigs are very thin designs carved into plaster and filled with white clay.  the white clay design is allowed to dry a little and then removed from the mold and stuck down onto the blue background.  they are very thin and that is why they look so good against the darker background.

 

the mold used for those thin sprigs are what i am talking about except that the shapes will be your leaves or petals and made much thicker.   if you have a rolling pin handy take a leaf from a houseplant or something else and put it on some flat clay about as thick as your little finger.  roll it down into the clay with your rolling pin.  take it out and you will see a hole in the slab in the shape of the leaf. that is your mold.  roll out a bunch of leaves or petals in various sizes.  take the biggest one out of the mold when it is dry enough to handle.  do that by pressing a damp piece of clay onto the back side of the leaf or petal.  pick it up and start making your assembly of leaves and petals.

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Chris Campbell    1,088

If you go to this link and scroll down to the second image you will see some small molds ....

 

http://ccpottery.com/villas/

 

Top and bottom are sprig molds and center ones are latex.

 

Each of your leaves could be individual sprig molds or multiples on one large slab of clay.

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oldlady    1,323

marvelous, chris!   i want to send this to my friend jan richardson who made a living building small houses for candles.  they were wonderful and still collectible, Windy Meadows Pottery.

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