Color Cement Handicraft

by Pedro J. Lemos; Reta A. Lemos

THE FIRST STEP, making the original model, is as follows: With clay or modeling wax build a form of the vase or bowl desired. The inside need not be considered; that is, do not make the form hollow but build it solid. Care should be taken to see that the contour is even and alike when viewed from all sides. A templet cut from metal, wood or stiff cardboard, will help in securing perfect contour if moved around on the outside and corrections made accordingly. A false neck should be added onto the solid form and part of the bottom of the mold scraped so as to leave a rim or edge on the bottom. The form is then ready to make a mold from it.

ANY VASE OR BOWL CAN BE DUPLICATED in cement by making a plaster mold from it. The inside of the bowl should be filled with sand or wadded paper and a false neck built over the mouth with clay or modeling wax. If the surface is glazed it need not be oiled before casting, but all dull or rough surfaces should be oiled.

THE SECOND STEP, making the molding case, is as follows: Take the model (clay or vase to be duplicated) and place it upon an oiled glass or other smooth surface. Marking off about one-third of its diameter, build a narrow strip of clay or wax on two sides from top to bottom. This ridge or wall should extend far enough out to meet the molding case or metal strip, and the two walls of clay and the metal or case should be made proof against the plaster running out anywhere, when it is poured into this well. After the plaster is set, the clay strip can be removed from one side and the exposed plaster edge is oiled after two keys have been bored into it with a pointed metal strip (see working plate). The removed strip is then built along the next division of the model and the case or metal used for retaining wall is moved into new position and a second third of the molding case is made. To make the third or last piece of the mold the two first sections are retained in position (always boring keys and oiling exposed edges), the case or metal wall again placed in position and the plaster poured into the opening. The plaster should not be too thin and if a little is poured into the bottom and allowed to set before pouring the whole amount, it will not be forced out through the bottom. Of course all openings must previously have been stopped with clay or wax.

TO STRENGTHEN A MOLD strips of burlap or wire screening can be imbedded in the plaster while it is soft. This makes a durable mold capable of withstanding much handling.

TO MAKE THE MOLD FOR THE BOTTOM the three sections are turned upside down (the model still being in position) and the plaster parts all being oiled, a ring of clay is placed around the bottom so as to make a cup shape into which the plaster is poured.

THE THIRD STEP is the most important part as the mixture or “slip” for the pouring is important. The first mixture should be neat cement and water and should be rather thick, for if too thin it will not adhere to the walls of the mold. When the neat cement is ready it should be poured into the bowl about half-way full. The bowl is then rotated in a horizontal position gradually downward so that the surplus cement slip will pour out of the mouth back into the pan or container in which it was mixed. Then after a half-hour or so another mixture of slip should be rotated. This mixture should be composed of a one-third cement and two-thirds sand mixture and be thinner in consistency. If the bowl is large and the walls need to be thick a third and fourth layer may be necessary.

THE LAST LAYER OF SLIP can be of neat cement which will finish the inside with a smooth surface. When working with color the first rotation and the last may have color added to the slip which will result in a color finish on the inside and the outside of the bowl or vase.

THE FOURTH STEP or releasing the mold, should occur the second or third day after the pouring has taken place. This elapse of time depends all upon weather conditions. In summer cement dries more rapidly and not so well. In winter the hardening is more slowly accomplished but more perfectly.

THE DRYING OF CEMENT is best when it occurs gradually. Never place cement in the sun or use artificial heat to force it. Checking, cracking and breaking will surely result if this is done.

For this reason the tiles and pottery made with cement should dry gradually in the shade but not in a draughty location.