Tamara Bonet Sculpture, Bronze and Ceramic Figurative Art
Bronze, Ceramic, About, and Contact

Relief Mold

Relief Mold

Hi All,

(Please see prior moldtutorial for in depth info)

Just a few more tips on mold making that I’ve learned:

  • When molding a water (earth) clay sculpture, evaporation will occur and create bubbles in the rubber.

I know this for a fact now.  It was very cold in the garage (even here in CA) and so little or no evaporation occured thus, I could apply the silicone rubber thicker on the first coat than I did during warm months.  Only problem is, the silicone cures very slowly, and if it gets too cold, risks not curing at all.  My first layer took a day and half or more to cure before I could put on the next layer.  Normally a day would be plenty long enough.

Just to test out the theory that evaporation is causing bubbles, I brought the mold inside where it’s warm and within minutes bubbles started to create.  Then I brought it outside and they stopped. 

In the past, I used a clear acrylic spray to seal in the moisture and thought that was good enough.  After bubbles were created I wondered if the silicone was reacting to the acrylic spray.  I found that it was not.  The moisture was finding it’s way out of that layer of spray.

 I did an experiment with another piece of clay, one part was thoroughly dry and the other was leather hard (still with moisture in it).  After spreading silicone over the whole piece, the silicone on the bone dry area was flat as can be – nice and smooth and no air bubbles.  The leather hard area had oogles of bubbles all over it.  Definitly moisture is what causes bubbles in my silicone rubber ( GI 1000 silicone). 

  • When applying your fiberglass that has been dipped into plaster onto your silicone rubber to make the mother mold, it’s best to first brush plaster all over the silicone first.  I learned this the hard way.  In a photo below you can see areas that were dry without enough plaster so that a hollow is created in the mother mold.  I earnestly tried to push the fiberglass onto the rubber as the plaster was setting up.  For the most part it attached itself well to fit the rubber.  Unfortunately there was a spot by the cheek on the face (important area) that didn’t squish in and had a gap.  So when I push on the silicone mold it gives way in that area.  Therefore, I backfilled with some more plaster/fiberglass.  As far as I can tell, the face hasn’t been altered too much by doing that.  EDIT- DO NOT DO THIS.  IT DID ALTER THE FACE- I had to scrape out what I had filled.  Not good!  Just let it be.  The plaster or wax won’t put enough pressure on the face to distort even though the mother mold wasn’t perfectly backing it up. 
  • Having your rubber at least 3/8 inch thick gives support to your mold in itself so that if there are small little areas where the mother mold isn’t pressing up tight, the mold will still hold up and not lose shape when casting. 
  • If those rubber keys (round tubes) don’t pull out of the mother mold very easily (even after using a lubricant like petroleum jelly) then a plaster rasp tool can be used to trim down the holes.  It’s good to have the keys lock in or snap in to place the rubber but they also need to pop out of the mother mold without a lot of effort.  They should snap in and snap out. 

Well, those are just a few points to share with you from this latest mold.  Hope it is of some help to you.

This pic below is similar to my other mold tutorial photos. You can see the back side of the clay wall is held up from falling by the use of  T pins.

Back side of clay wall held up with t pins.

Back side of clay wall held up with t pins.

Clay wall is read for plaster and fiberglass to be applied.

Clay wall is read for plaster and fiberglass to be applied.

I may be doing overkill on those keys by adding too many but hey, it works for me. I do think that if they rubber is thick enough then less keys is in order. The flimsier the silicone is because of being too thin, the more it needs to be held in place with keys. The front side of my silicone mold was plenty thick but the back side is probably a little under the 3/8 recommended thickness. I won’t do that again. On this relief it doesn’t hurt though.

Mold is ready for back side to be applied.

Mold is ready for back side to be applied.

Next pics I skip ahead after the mold is completed and original has been taken out.

Plaster cast is ready to be taken out.

Plaster cast is ready to be taken out.

While the garage is a mess is a good time to go ahead and try out the mold right away and see how it turned out. This plaster cast was ready to be taken out after a day. If it was a bigger cast then it would be good to even wait 2 days so that the plaster can harden and have less chance of breaking while demolding.

Demolding the plaster cast.

Demolding the plaster cast.

Plaster cast is partialy revealed.

Plaster cast is partialy revealed.

The plaster came out nearly perfect with the smoothest skin. I’m very happy with how well the mold turned out. The original sustained damage as usual. That’s okay I’ll fix her back up and fire and glaze her. :-)

Clay original was damaged when the mold was taken off.

Clay original was damaged when the mold was taken off.

Plaster came out very well with smooth skin and no air bubbles.

Plaster came out very well with smooth skin and no air bubbles.

Area below writing was filled in with fiberglass and plaster.

Area below writing was filled in with fiberglass and plaster.

 (See EDIT above regarding not filling in a spot on the mother mold in a critical place such as the face.)

Thanks for watching everyone. Your comments are always appreciated.

~Tamara

3 Responses to “Relief Mold”

  1. ZooDoc says:

    Very interesting. Thanks for sharing. ZD

  2. Maria Hyman says:

    Hi Tamara, I saw you at the Sacramento Art Festival in 2009 and was very taken with the sculpture of the Indian Woman in a canoe. What ever happened to that piece? Do you have a photo of the finished product?

    Thank you.

  3. Tamara Bonet says:

    Thanks for commenting Maria.
    Funny you should ask about that sculpture…. :-) I recently had someone else ask about her too. Actually I got sidetracked but she is still waiting to be finished. Here’s some updated pics of her on my blog though: http://tamarabonet.com/blog/2010/03/16/american-indian-woman-sculpture-art/#more-597

Leave a Reply

tamarabonet.comHelp Stop Art Fraud
Email: tamarasculpture@sbcglobal.net
Bronze Gallery Ceramic Gallery About Tamara Bonêt Contact Tamara Bonêt Help Stop Art Fraud