Wednesday, 15 October 2014

#574 The studio in Canada: more about making molds . . .

The previous blog is about the creation of the Cody quick-draw bull that was transported to the island studio in 
Canada last month and the clay model can be seen on that post . . .  this post follows the mold making process.  
Mold making was discussed in post # 572, October 8, 2014.  Today's post will supplement 
# 572 with additional data and tips about making flexible parting molds.  
Please review the basic mold making procedure in post # 572.

The focus of this blog includes a more in-depth presentation about SHIMMING THE RUBBER MOLD to make a parting line or seam.  While the shimming process was discussed in post #572,  this blog will include Trish's tips - based upon over 20 years of experience - for making a flexible parting mold.

Last year, Trish taught mold making in conjunction with one of my bird sculpture and anatomy workshops.
We both learned that by far, the shimming and creation of a seam line or parting line in order to open
the mold is the most difficult concept to understand for beginning students.

Simply put:  The rubber mold must be shimmed to create a parting line or seam. . . this seam is where the mold
is divided into two sides.   The mold must be parted or separated to remove the wax replica of the sculpture
after liquid wax has been poured into the mold and cooled.

At right, the Cody bull is shown with the first coat of rubber being applied. Please refer to the previous  post for information about the creation of this sculpture.

Trish's tip:  Note the rope of clay that surrounds the model on the mold board . . . this serves as a "dam" to catch the rubber before it cures and sets up.

Shown at right, two coats of rubber have been applied, have setup and cured and the mold is now ready to shim . . .
shimming is done before the third coat of rubber.

Trish's tip:  Draw lines on the sculpture to approximate where the shims will be placed and the mold will separate . . . be careful not to make the parting seam across sensitive areas - such as eyes or deep negatives - that the artist has modeled.

Shown at right, wax-coated paper cups are cut and flattened out.  The "keys" are plastic trays that pharmacists use in drugstores to hold pills.  The keys lock the two sides together.

The paper cup shim is cut into a shape that follows the figure as shown below.  Keys are  inserted into the shim by cutting a rectangle so the key fits snug.  . . use an x-acto knife here.  The key is then taped down on all sides. The shim is applied to the outside of the rubber mold along the seam and attached into the rubber with dressmaker pins.

Below, the keyed shim pieces are taped and stapled together forming a continuous seam.
A piece of sprue wax has been added between the figure's leg and tail . . . this "gate" or channel will cause the liquid wax to flow into the outer portions of the mold more effectively.
Note the wax pour spout behind the figure's left leg and centered on the belly.

Above, the shimming has been completed and the thick shim coat - coat # 3 - will be applied.
The last coat is applied after the shim coat sets up and cures.

Trish's tip:  Use the best pair of scissors you can afford . . . I use a small pair of German 
quilter's scissors and a larger pair of Case shears.

Trish's tip:  Take the extra time to do it right . . . no short cuts.  

Remember - the mold is now the original of the sculptor's creation.

Note:  Before hot, liquid wax is poured into the mold, the two sides of the rubber mold must be encased in a plaster "mother-mold" to give rigidity and support to the flexible rubber.   After the liquid wax is poured into the mold and
has cooled, the two sides must be divided or separated and the wax replica of the artist's sculpture is removed.
Making a mother-mold will be discussed at a later date.

Molding and sculpture supplies are available at Sculpture Depot in Loveland, Colorado.

Go to the BLOG INDEX on the right for more information. 

Blog, text, photos, drawings, and sculpture . . . © Sandy Scott and Trish

No comments:

Post a Comment