In a New Mold: Steps for casting plaster ornament

July 1, 2003

Lenox, MA (July 1, 2003) --

by Gordon Bock and Jeffrey P. Gulick

Molds of many kinds have been used for centuries for making interior ornaments from plaster. In new construction, molds make it possible to turn out multiple, identical castings of the same design ‑ a process that is both efficient and necessary where, for instance, the interior architecture requires scores of rosettes marching around a ceiling or a chain of swags ringing a room. Besides being a traditional technique in building restoration, molds have the added advantage of providing an ideal way to faithfully replace and duplicate missing or damaged plaster ornaments after the original source is gone.

 

An example of this work is the elegant, classically styled dining room at The Mount in Lenox, Massachusetts. When author Edith Wharton completed her dream house around 1902, the dining room walls were decorated with sculpted plaster garlands designed by Ogden Codman, her architect friend and coauthor of the book The Decoration of Houses. Some 80 years of building changes and varied ownerships later, however, little more than ghostly outlines of the garlands remained. When the building's current stewards, Edith Wharton Restoration, Inc., decided to restore the room in 2001, master sculptor and mold maker Jeff Gulick was on hand to help. Here are the techniques he used to mold new decorative hanging garlands, the central theme of the room, from intact originals.

 

The Plaster Problem

 

After researching the size and pattern of the dining room garlands, Jeff chose to base the reproductions on the best existing example in the building: a section of Codman‑designed garlands of the same scale in an adjacent room. To capture this design, Jeff turned to moulage ‑ a French term for the general process of making an impression. Historically, moulage could be made with natural materials such as animal gelatin. For this project Jeff decided to work with agar (also known as agar‑agar), a plant gelatin made from seaweed found in Malaysia. Originally popular for making molds for false teeth, agar provides excellent reproduction of detail and great flexibility (it means "sticky jelly" in Malaysian). Jeff chose agar for molding the historic garland not only for its ability to form around all the intricate decorations, but also because the jellylike material sets up quickly‑ideal for working on a vertical surface. More important, it is least likely to stick to the plaster and damage delicate features, which is a risk with rubber molding materials. "Agar is used for casting face masks from life for the same reason," says Jeff. Jeff begins by cooking up the agar. To keep from drying out the material, it has to be heated with water in a double boiler. Jeff has previously removed all paint from the garland and cleaned the surface down to the original plaster, but other than this, agar requires no preparation or mold release agent. "In the old days," says Jeff, "they used to cook up a mixture of wax or paraffin dissolved in turpentine and apply it to the plaster as a mold release" Jeff does, however, build a frame of light lattice around the ornament to define the perimeter and depth of the mold.

 

Then, while the agar is still warm, he brushes it quickly onto the model garland. Jeff works from the bottom up to make sure he gets the agar into all the crevasses and undercuts. (Working from the top down, the material will skip over recesses in the mold.) It's quick work. Once the plaster and agar make contact, the agar cools, taking only five or six minutes to set up. The hardest part is keeping the material on the high points of the plaster, where it tends to run off. After building up a coat about 1/8" thick, Jeff returns immediately to fill in the deep areas with an artist's spatula. Then, while the rest of the mold is still wet, he dunks a section of cheesecloth in the agar and slaps it over the just‑applied layers. He holds the cheesecloth in place until the gelatin sets. The cheesecloth adds integrity to the agar and keeps the mold from tearing in the following steps.

 

At this point the agar will have captured all the carved details of the ornament, but because it is so flexible, it will easily distort and be difficult to handle as a mold. To give the necessary support, Jeff's next step is to create a mother mold on top of the agar. Dipping a length of burlap fabric in a batch of soupy molding plaster, he applies it on top and forms it to the gelatin so that, when the plaster hardens after 20 minutes, it becomes a cradle for the supple gelatin, helping the gelatin retain the correct form and plane.

 

When the agar and plaster are ready, Jeff removes them from the wall by cleaning away any material spilling over the frame and gently disassembling the frame itself. Working carefully, he wiggles his fingers behind the ornament grouping and frees the agar mold from the plaster. The agar comes off cleanly, bringing with it an exact impression of the original garlands.

 

Casting Around

 

Jeff's next move is not, as one might expect, to begin producing a batch of replication ornaments, but instead to cast a new original plaster garland from which he will make another mold. (While the agar is ideal for accuracy and gentleness it is not tough enough to last for scores of castings over many years.) For this step Jeff fills the agar mold with #1 molding plaster mixed to a creamy consistency, and submerges pieces of cheesecloth in the delicate areas to add strength to the casting. Jeff chooses molding plaster for this step because it is relatively soft and he can tool it later to clean up details or correct imperfections. Once again, the jellylike agar will separate cleanly from the plaster without his adding any lubricants.

 

Once he has an original ornament, Jeff is ready to make the final rubber mold that he will use to cast the many pieces needed to re‑create the complete garlands. Jeff's first step is to build a wood "dam" system around the new casting so that the rubber won't leak out and the final mold will extend beyond the ornament itself for convenient casting. Working on a table saw, Jeff cuts 2x4 lumber into L‑shaped sticks similar to angle irons. These will be placed around the plaster to form a box. When the box is around the casting, Jeff fills in cracks and breaches of any kind with more plaster. "The liquid rubber is very pervasive," he says, "and will immediately run out through any pin holes." Last, he shellacs, then waxes all surfaces of the casting and box to make sure the rubber will separate without problems ‑ going as far as the "belt‑and‑suspenders" approach of a final spray of silicone release agent. "You want the most perfect surface you can get,” he says.

 

To pour permanent rubber molds like this, Jeff likes a polyurethane rubber product (Polytek 78) because it's inexpensive and easy to use. "Rubber bends; that's the advantage" he says. "The old way to cast ornamental plaster was with solid‑piece molds‑similar to those used in metal casting. In addition, the finished mold should last 10 years ‑ part of the larger plan for the reproduction ornaments once the room is done.

 

Jeff switches to Hydrocal plaster reinforced with cheesecloth for casting actual reproduction garlands. While Hydrocal expands a bit more than molding plaster as it cures, it produces a much harder final product, and it assures that delicate details unmold intact, even with the recommended releasing agent. Using this procedure, Jeff goes on to cast the 84 pieces required to complete the missing garlands ‑ each composed of seven separate groupings or pieces.

 

Final Details

 

Reproducing an original garland from elsewhere in the building is actually just the beginning of creating the restored dining room garlands. Evidence, such as paint ghosts on the walls, indicates that each garland was actually 9" longer than any existing examples. Moreover, the overall designs at first glance appear to be identical but actually vary subtly in left and right versions incorporating, say, a bunch of grapes in a left‑hand version, walnuts in the right‑hand version. The result is an asymmetrical but balanced pair of ornaments that can be used on either side of a door or in a left‑right‑left‑right motif across a wall. Re‑creating this variation, as well as extending the pattern, means Jeff has to borrow new elements (flowers, fruits) of the same visual weight from yet another source. He replicates sections of a similar, and still intact, garland from another room by using the same moulage technique.

 

Originally, the old ornaments were attached to the wall with molten shellac ‑ a method that allowed the plasterers to secure the various components quickly, but it was a method that may have led to their loss when the bond eventually failed. Jeff chooses to avoid this potential problem a century later by gluing the pieces up with knifeable grade polyester resin, a transparent paste that sticks readily to a vertical surface. After mixing the catalyst, Jeff "butters‑up" the back of each ornament, positions it on the wall, and holds it in place until the resin sets. “I mix the catalyst/resin ratio a little on the hot side so it sets up in seven or eight minutes," says Jeff. Once every ele­ment of garland is in place, Jeff’s last step is to brush the void between casting and wall with a coating of molding plaster fol­lowed by a brushing of water. "This is called 'killing the plaster," says Jeff. The procedure's purpose is three‑fold: 1) to fill in the void behind the ornament for cos­metic reasons, 2) to create a capillary system that joins the wall plaster and the ornament plaster, 3) to take the "heat" out of the ornament's plaster ‑ that is, completing the chemical reaction in the casting so it doesn't crack in the future. The multiple rubber molds will continue to be in active service for many years to come. "They'll be used in the gift shop for turning out souvenir ornaments ‑ just like the ones in the dining room," says Jeff.

In a New Mold: Steps for casting plaster ornament.

 

by Gordon Bock and Jeffrey P. Gulick

 

Molds of many kinds have been used for centuries for making interior ornaments from plaster. In new construction, molds make it possible to turn out multiple, identical castings of the same design ‑ a process that is both efficient and necessary where, for instance, the interior architecture requires scores of rosettes marching around a ceiling or a chain of swags ringing a room. Besides being a traditional technique in building restoration, molds have the added advantage of providing an ideal way to faithfully replace and duplicate missing or damaged plaster ornaments after the original source is gone.

 

An example of this work is the elegant, classically styled dining room at The Mount in Lenox, Massachusetts. When author Edith Wharton completed her dream house around 1902, the dining room walls were decorated with sculpted plaster garlands designed by Ogden Codman, her architect friend and coauthor of the book The Decoration of Houses. Some 80 years of building changes and varied ownerships later, however, little more than ghostly outlines of the garlands remained. When the building's current stewards, Edith Wharton Restoration, Inc., decided to restore the room in 2001, master sculptor and mold maker Jeff Gulick was on hand to help. Here are the techniques he used to mold new decorative hanging garlands, the central theme of the room, from intact originals.

 

The Plaster Problem

 

After researching the size and pattern of the dining room garlands, Jeff chose to base the reproductions on the best existing example in the building: a section of Codman‑designed garlands of the same scale in an adjacent room. To capture this design, Jeff turned to moulage ‑ a French term for the general process of making an impression. Historically, moulage could be made with natural materials such as animal gelatin. For this project Jeff decided to work with agar (also known as agar‑agar), a plant gelatin made from seaweed found in Malaysia. Originally popular for making molds for false teeth, agar provides excellent reproduction of detail and great flexibility (it means "sticky jelly" in Malaysian). Jeff chose agar for molding the historic garland not only for its ability to form around all the intricate decorations, but also because the jellylike material sets up quickly‑ideal for working on a vertical surface. More important, it is least likely to stick to the plaster and damage delicate features, which is a risk with rubber molding materials. "Agar is used for casting face masks from life for the same reason," says Jeff. Jeff begins by cooking up the agar. To keep from drying out the material, it has to be heated with water in a double boiler. Jeff has previously removed all paint from the garland and cleaned the surface down to the original plaster, but other than this, agar requires no preparation or mold release agent. "In the old days," says Jeff, "they used to cook up a mixture of wax or paraffin dissolved in turpentine and apply it to the plaster as a mold release" Jeff does, however, build a frame of light lattice around the ornament to define the perimeter and depth of the mold.

 

Then, while the agar is still warm, he brushes it quickly onto the model garland. Jeff works from the bottom up to make sure he gets the agar into all the crevasses and undercuts. (Working from the top down, the material will skip over recesses in the mold.) It's quick work. Once the plaster and agar make contact, the agar cools, taking only five or six minutes to set up. The hardest part is keeping the material on the high points of the plaster, where it tends to run off. After building up a coat about 1/8" thick, Jeff returns immediately to fill in the deep areas with an artist's spatula. Then, while the rest of the mold is still wet, he dunks a section of cheesecloth in the agar and slaps it over the just‑applied layers. He holds the cheesecloth in place until the gelatin sets. The cheesecloth adds integrity to the agar and keeps the mold from tearing in the following steps.

 

At this point the agar will have captured all the carved details of the ornament, but because it is so flexible, it will easily distort and be difficult to handle as a mold. To give the necessary support, Jeff's next step is to create a mother mold on top of the agar. Dipping a length of burlap fabric in a batch of soupy molding plaster, he applies it on top and forms it to the gelatin so that, when the plaster hardens after 20 minutes, it becomes a cradle for the supple gelatin, helping the gelatin retain the correct form and plane.

 

When the agar and plaster are ready, Jeff removes them from the wall by cleaning away any material spilling over the frame and gently disassembling the frame itself. Working carefully, he wiggles his fingers behind the ornament grouping and frees the agar mold from the plaster. The agar comes off cleanly, bringing with it an exact impression of the original garlands.

 

Casting Around

 

Jeff's next move is not, as one might expect, to begin producing a batch of replication ornaments, but instead to cast a new original plaster garland from which he will make another mold. (While the agar is ideal for accuracy and gentleness it is not tough enough to last for scores of castings over many years.) For this step Jeff fills the agar mold with #1 molding plaster mixed to a creamy consistency, and submerges pieces of cheesecloth in the delicate areas to add strength to the casting. Jeff chooses molding plaster for this step because it is relatively soft and he can tool it later to clean up details or correct imperfections. Once again, the jellylike agar will separate cleanly from the plaster without his adding any lubricants.

 

Once he has an original ornament, Jeff is ready to make the final rubber mold that he will use to cast the many pieces needed to re‑create the complete garlands. Jeff's first step is to build a wood "dam" system around the new casting so that the rubber won't leak out and the final mold will extend beyond the ornament itself for convenient casting. Working on a table saw, Jeff cuts 2x4 lumber into L‑shaped sticks similar to angle irons. These will be placed around the plaster to form a box. When the box is around the casting, Jeff fills in cracks and breaches of any kind with more plaster. "The liquid rubber is very pervasive," he says, "and will immediately run out through any pin holes." Last, he shellacs, then waxes all surfaces of the casting and box to make sure the rubber will separate without problems ‑ going as far as the "belt‑and‑suspenders" approach of a final spray of silicone release agent. "You want the most perfect surface you can get,” he says.

 

To pour permanent rubber molds like this, Jeff likes a polyurethane rubber product (Polytek 78) because it's inexpensive and easy to use. "Rubber bends; that's the advantage" he says. "The old way to cast ornamental plaster was with solid‑piece molds‑similar to those used in metal casting. In addition, the finished mold should last 10 years ‑ part of the larger plan for the reproduction ornaments once the room is done.

 

Jeff switches to Hydrocal plaster reinforced with cheesecloth for casting actual reproduction garlands. While Hydrocal expands a bit more than molding plaster as it cures, it produces a much harder final product, and it assures that delicate details unmold intact, even with the recommended releasing agent. Using this procedure, Jeff goes on to cast the 84 pieces required to complete the missing garlands ‑ each composed of seven separate groupings or pieces.

 

Final Details

 

Reproducing an original garland from elsewhere in the building is actually just the beginning of creating the restored dining room garlands. Evidence, such as paint ghosts on the walls, indicates that each garland was actually 9" longer than any existing examples. Moreover, the overall designs at first glance appear to be identical but actually vary subtly in left and right versions incorporating, say, a bunch of grapes in a left‑hand version, walnuts in the right‑hand version. The result is an asymmetrical but balanced pair of ornaments that can be used on either side of a door or in a left‑right‑left‑right motif across a wall. Re‑creating this variation, as well as extending the pattern, means Jeff has to borrow new elements (flowers, fruits) of the same visual weight from yet another source. He replicates sections of a similar, and still intact, garland from another room by using the same moulage technique.

 

Originally, the old ornaments were attached to the wall with molten shellac ‑ a method that allowed the plasterers to secure the various components quickly, but it was a method that may have led to their loss when the bond eventually failed. Jeff chooses to avoid this potential problem a century later by gluing the pieces up with knifeable grade polyester resin, a transparent paste that sticks readily to a vertical surface. After mixing the catalyst, Jeff "butters‑up" the back of each ornament, positions it on the wall, and holds it in place until the resin sets. “I mix the catalyst/resin ratio a little on the hot side so it sets up in seven or eight minutes," says Jeff. Once every ele­ment of garland is in place, Jeff’s last step is to brush the void between casting and wall with a coating of molding plaster fol­lowed by a brushing of water. "This is called 'killing the plaster," says Jeff. The procedure's purpose is three‑fold: 1) to fill in the void behind the ornament for cos­metic reasons, 2) to create a capillary system that joins the wall plaster and the ornament plaster, 3) to take the "heat" out of the ornament's plaster ‑ that is, completing the chemical reaction in the casting so it doesn't crack in the future. The multiple rubber molds will continue to be in active service for many years to come. "They'll be used in the gift shop for turning out souvenir ornaments ‑ just like the ones in the dining room," says Jeff.