The Art of Stone Casting: The Boundless Borders of Architectural Creations
Picking up a stone pineapple finial with a finish appearing to be hundreds of years old, a client of mine asked, “Is this natural limestone or concrete?” Smiling, because I am asked this question often as a historical garden element consultant, “Neither,” I replied, “It is made of cast stone, a refined architectural art form hand made from castings comprised of Portland cement and a high percentage of a variety of finely crushed stones. The detailed beauty of a cast stone piece’s final form depends on the skills of its maker and the quality of the mold it is cast from.” Expertly crafted and stained cast stone can fool even the most studied eye into believing the object is carved from natural limestone. The masonry techniques used to create fine cast stone architectural elements is an art form that dates back thousands of years. The stunning European remains of the cast stone wall surrounding the medieval city of Carcassonne, France, built in 1138, indicate the resilience of cast stone over time. The Romans created masterpieces made of cast stone choosing it over carved stone for its beauty and durability. Still today, cast stone is a building material of choice by high-end architects seeking enduring and opulent details for large-scale constructions at affordable prices.
Although many would consider marble, because of its intrinsic beauty, as a more desirable medium for architectural elements, it is expensive to carve and does not hold up well to the test of time. In northern Europe due to the frigid winters, elaborate installations of 17th- and 18th-century Italian marble became damaged in outdoor settings.
In pursuit of a more cost effective and durable medium for castings, Eleanor Coade in the late 1700s in her factory in Lambeth, England, created Coade stone, a fired clay stone aggregate that was produced using the dry cast method. The stone pieces were then fired at high temperatures capturing the exceptional detail of the original pieces. She not only copied natural stone but also antique garden ornaments such as the Medici and Borghese urns and many classical cherubs and mythological figures. Because Coade stone was impervious to frost and less expensive than carved stone, it also became popular as the material used in the building of large-scale projects.
However, it was not until the 1900s in England that cast stone was predominantly used in the construction of buildings. Cast stone became a perfect replacement material for brownstone and limestone facades. Its natural look blended well with the carved stone originals thus making it an acceptable and affordable architectural replacement for design. The popularity of cast stone as not only a building material but as a medium for garden ornaments reached America during the Industrial revolution where it has been widely used ever since.
Today, contemporary cast stone has changed little over time. Except for a few variations or enhancements used in the mixture, the techniques used to produce this product that emulates nature are still the same as those used thousands of years ago.
Frequently, contractors are confused about the difference between architectural precast concrete and cast stone. Although they are both made of basically the same materials, they are produced using two distinct methods. Typically, the precast concrete is used for larger architectural products while the cast stone is used for smaller, nonstructural pieces such as ornamental details. The wet cast method is used for architectural precast structures and is produced with a pourable concrete that is rated by a slump test for its durability. The cast stone is produced by the vibra dry tamp method where there is virtually no slump in the product at all. The molds used in the wet cast method must be tapped for air pockets and the mixtures are allowed to remain till the item is dry the next day. In the vibra dry tamp method, the piece is immediately taken from the forms after compaction and removed into a curing room for a day or two. Each method has its appropriate application, however, the vibra dry tamp method is used for finer pieces where there is a need for exceptional detail and sometimes a smoother finish.
The finest cast stone pieces used for balusters, balls, or columns should be hand finished by the manufacturer eliminating unsightly seams and ridges. Of course, these superior pieces are more costly. However, it is the artist’s attention to the details of each piece that can create the illusion of natural stone.
In addition to building materials, examples of these different products of casting can be found in classic garden statuary, fountains, and ornaments. The less expensive mass-produced garden elements usually bare the signs of mold lines and the detail on the castings are not as crisp.
Molds can be used for only a limited number of castings. Depending on the thickness of the mold’s lining, the castings become less defined after usually two hundred or more pours. The features on statues become less pronounced if the mold is near the end of its use. A skilled artisan can stretch the use of a mold by properly seasoning the mold after each use.
Special acids can be used on the stone castings after they are produced to create a weathered and ancient appearance. Some artisans choose to mix a tint into the mixture before it is poured into the mold. When the mixture is tinted in this fashion, the chosen color is saturated through the finished stone. The drawback in this method is that there is less opportunity for the artist to give variations to the color with acids since the stone is already tinted.
Stone casting offers endless possibilities to reproduce forms. It is an ancient art that can unleash the imagination through the skilled hands of its creators. It offers a strong and creative medium for any architect or homeowner carving out their dreams for the future. ✦
