A 3-dimensional sculpture of Joe Brown, Professor of Sculpture for Princeton University, was created by Tim Maslyn of Maslyn Studios. The goal is to reproduce this casting in a plaster modified gypsum.
The supplies: Brush-On® 40, SuperSeal® sealing agent, Universal® Mold Release, So-Strong® Blue Tint, Cab-O-Sil, mixing cups, gloves, glue gun, paper towels, brushes, safety glasses, and mixing sticks.
The bust is glued down to the work surface.
Brush-On® 40 is a urethane rubber. Urethanes are adhesive and will stick to most surfaces. A sealing agent followed by a release agent is required for mold models. SuperSeal® sealing agent is applied to the plaster bust.
SuperSeal® is also applied to the wooden platform.
Universal® Mold Release is applied to the bust and the platform.
The mix ratio of Brush-On 40 is 1A:1B by volume. One cup of Part A liquid is measured out.
One cup of the Part B paste is measured out. Be careful to pack the paste into the cup and eliminate any air voids.
Combine Part A with Part B in a mixing container.
Since the original model is white and the mold rubber is white, SO-Strong® Blue Tint is added to this first mix of rubber to help ensure thorough coverage over the model.
Parts A and B are mixed thoroughly. The blue color also acts as a positive mix indicator. When all color streaks are eliminated, that is an indication that the rubber is properly mixed.
DO NOT OVER APPLY!The first coat, called the "detail coat," is applied very thin. This will enable the first layer of rubber to de-air itself. If you over apply, bubbles will be trapped in the first layer which will result in bubbles in the finished casting.
Working from the top down, continue applying a thin first layer of rubber over the entire model. Use a 'stipple' application technique to ensure that the rubber works its way into all surface detail.
Cover the entire model and bring the rubber out to the edge of the platform, at least 3 inches / 7.62 cm from the base. This "flange" will help register the rubber mold with the support shell later in the mold making process. Once you are finished applying rubber, check to make sure you did not miss any areas.
Allow the rubber to become "tacky", which means sticky to the touch but will not come off on your gloved finger. After 30 minutes at room temperature, touch the rubber "off model" to test. If it's still wet and comes off on your glove, let it continue to cure. If the rubber is sticky and does not come off on your glove, you are ready to apply the next layer.
Second Layer; Mix and apply the second coat of rubber, this time without color. This layer is applied a little thicker with free-flowing strokes.
Once the model is covered with the second coat, carefully check to make sure all areas are covered. Allow the rubber to become 'tacky' before moving on the next step.
Layer 2.5 - CabOSil is fumed silica that is often used as a mold rubber. It will be used to thicken the Brush-On rubber for the purpose of filling in undercuts and building a "cut-shim".
A safety mask is worn to prevent inhalation of the Cab-O-Sil powder.
Cab-O-Sil is then added a little at a time until the right 'thixotropy' is attained.
The pigmented Brush-On® 40 and Cab-O-Sil are mixed well. The rubber is notably thicker approaching the consistency of bread dough.
Begin building a 'cut seam'; the rubber mold wll be removed from the model by cutting. We will cut the rubber along a thickened cut seam which will aid in registering the cut areas of the rubber when it comes time to cast into the mold. Starting at the top of the head and working straight down the back, the cust seam is applied.
The thickened rubber is also used to make a registration key around the perimeter of the mold. The thickened rubber is also used to fill in undercuts and indentations. This will make removal of the support shell much easier later.
The thickened rubber is used to fill undercuts such as the eyes, ears and nostrils. This again will help avoid mechanical lock between the model and support shell.
Third Coat: Rubber is mixed, pigmented red, and applied over model including the thickened rubber.
After the third coat, check to ensure thorough coverage.
Coat 3.5 - More thickened rubber. Another batch of rubber is mixed without pigment. Cab-O-Sil® is added as before and the right consistency is attained.
The cut seam is built up with the Cab-O-Sil® thickened rubber.
The eyes, nose and ears are filled again with Cab-O-Sil® thickened rubber.
4th Coat - Brush-On 40® is measured and mixed without pigement or CabOSil and the final coat of rubber iss applied. Following the 4th coat, all layers are allowed to cure overnight.
Next Day; Applying the Support Shell. Materials for Pasti-Paste® Support Shell: Sonite® Wax, Universal® Mold Release, Plasti-Paste®, non-sulfur clay, measuring cups, gloves, safety glasses, metal scraper, mixing sticks, plastic scraper and marker.
Study your model and develop a plan of attack for applying the support shell including the number of shell segments. The goal is to not have the rigid mother mold lock onto the rigid model. For this model, a three-piece mother mold is pre-planned.
Trim the flange of the rubber to create a clean edge. This will help the rubber mold register with the mother mold during casting.
Mapping out the support shell segments - The first line is drawn from the top of the head down over the high point of the ear, continuing over the high points of the shoulder and down to the outer edge of the mold.
An identical line is drawn down the opposite side of the mold along the high points to the outer edge of the mold.
A third line is drawn down the front of the mold, starting at the head and continuing down the center of the nose, over the chin and to the outer edge.
This image illustrates the defined 3 segments of the support shell.
Creating a parting shim for the applying the molther mold material - Chavant non sulfur clay is used to separate the support shell into sections.
The clay is applied at the line that separates the back of the bust from the front.
Pieces of clay are used to brace the clay wall from behind.
The back of the model will be the first to receive the Plasti-Paste® molther mold material.
As a final step prior to preparing the shell, a channel or "key" is carved into the clay using a paper clip. The key will help register shell segments together.
Plasti-Paste will bond to the Brush-On 40 urethane rubber. A combination of Sonite® II Wax and mold release is required to release the plastic from the rubber and plastic segments from each other.Sonite Wax is applied to the rubber and modeling clay and allowed to dry for 15 minutes.
Universal® Mold Release is then applied over all surfaces.
Plasti-Paste® is mixed 1 part A to 3 parts B by volume.
Parts A and B are mixed thoroughly.
Plasti-Paste® is applied to the surface of the rubber mold and out to the outer edge of the clay shim. It hold a vertical surface unlike any other trowelable plastic available.
Apply evenly and be sure to build up the outer edges. Finished support shell thickness is 3/8" or 1 cm. Plasti Paste sticks to itself well. Don't mix more than you can apply in 10 minutes. You can always mix and apply more.
The first segment of the the Plasti-Paste® shell is allowed to cure for 90 minutes. As it becomes rigid, it changes from dark to light in color.
After 90 minutes, the clay shim is removed from the first part of the Plasti-Paste® support shell.
Another clay shim is built along the pre-drawn line running from the top of the head down the front of the face.
The shim is reinforced on one side to support it when applying the Plasti Paste®.
Brush Sonite® Wax over all surfaces and let dry for 15 minutes.
Apply Universal® Mold Release over all surfaces.
Plasti-Paste® is mixed and applied as before creating the second shell segment.
Working from top to bottom, apply an even layer and build up to 3/8" or 1 cm thickness.
Allow the second shell segment to cure for 90 minutes.
The clay is removed exposing cured Plasti-Paste on two segments. Sonite® Wax is appled to the last exposed area of the the rubber and shell.
Universal® Mold Release is applied to all surfaces.
The third segment of the Plasti-Paste® shell is mixed and applied. Wait for it to cure 90 minutes before demolding all segments.
Removing the Shell: A screwdriver and hammer are used to slowly pry apart shell segments.
Section 3 is successfully removed.
Section 2 is removed from the model.
The final section of the mother mold is removed.
Using a razor knife, the rubber mold is carefully cut along the cut seam. An extra pair of helping hands assists in holding the mold open as it is cut.
The cut is made to the top of the head.
The mold is then carefully removed from the model.
The Brush-On® mold has perfectly captured all of the detail of the original.
The mold and the three sections of the support shell are layed out in preparation of casting.
CASTING: Spray the inside and outside of the rubber mold with Universal® Mold Release. Also apply release agent to all areas of the support shell.
Seat the mold into the Plasti-Paste® shell. The built up cut seam of the rubber mold registers perfectly with the channel in the support shell.
Mold straps are used to secure support shell segments around rubber mold.
Matrix® NEO® is a polymer modifed gypsum that is easy to use and cures to a tough, hard plaster. It is mixed 2 Parts A to 1 Part B by volume.
The goal in making this casting is to make it hollow and lightweight. The NEO® is poured into the mold cavity and the mold is rotated allowing the NEO to build up against the mold walls.
The mold is rotated allowing the batches of NEO to build in layers on itself.
Additional batches of NEO® are mixed and poured into the mold.
After the final batch of NEO® is mixed and rotationally cast into the mold, all layers are allowed to cure for at least an hour. The mold straps are then removed from the mother mold.
The sections of the shell are removed.
The mold is carefully separated at the back . . .
. . . and removed from around the casting.
The casting is a perfect copy of the original model and the mold is ready for casting again.
The casting is displayed next to the original sculpture and reflects perfect detail captured by the Brush-On® 40 mold.