Introduction: 3D Print Turned to Glass!
3D printing allows us to create very useful tools, but it can also allow us to create beautiful objects. 3D printing does not need to be the last step. This is a general guide to combining the hi tech practice of 3D printing with more historical craft practices. We can use 3D printed objects and make replicas made of solid glass through a casting process similar to metal foundry.
This process is, unfortunately, very difficult for the average maker because of the expensive equipment required. A wide variety of materials are also necessary. Some of these problems can be solved through studios that rent out equipment and materials. However, while not everyone can create glass objects, I hope that this helps inspire people to think about the variety of possibilities 3D printing offers us.
Step 1: Making a Mold From a 3D Print
Just like casting metal, we need to have objects made out of wax in order to cast molten glass. Some high end printers can now print directly in wax, but that is not necessary for this project. Once we have a printed object, we have to make a multi-part mold around it made from rubber. The rubber will capture all the details of the object and allow us to pour hot wax and create copies of this object.
A two-part mold is the easiest kind of mold. Using clay, plasticine, or a flat surface such as foam board, create a wall around half of an object. Using a liquid rubber such as Polytek, cover a surface completely and allow the liquid to set. once the rubber is no longer a liquid, we can pour plaster over the rubber to create a solid backing that will keep the rubber from bending or distorting when we pour hot wax into the mold.
For more complex shapes, sometimes we need to make molds out of three or more parts. This is an important step in order to avoid undercuts. Once every part is complete, take the mold apart and remove the 3D printed object. the mold should fit back together, leaving an empty space in the shape of the 3D print.
Step 2: Wax!
Now that we have our mold, we can pour molten wax into it! Wax will pick up all of the details that the mold has. The advantage of using wax is the ability to create replicas at a fast pace. It will always be faster to pour wax into a mold and let it cool than printing a new object. Wax replicas can also be augmented. In these images, I have taken a decorative hemisphere and connected two copies together to create a sphere.
When the wax is finished, we have to surround it with a mixture of plaster and silica in order to prepare it for the kiln. The wax shown above is elevated in order to create a pour spout for hot glass to enter. This mass of plasticine will become an opening and the whole object will be flipped upside down when it is in the kiln. Just like with metal casting, there has to be vents for air to escape as the glass enters the empty space.
Create a mixture of equal parts water, plaster, and silica. This mixture can either be poured around the wax or applied in layers by hand or brush. For casting glass, the plaster-silica should surround the wax and add an additional 4cm on every side. Cover the plaster-silica casing and let it sit overnight. Later, the wax has to be heated up and steamed out of the plaster-silica in order to create an empty space for the molten glass to fill. When all the wax is gone, put the mold into a kiln so that it can dry completely.
Step 3: Casting Glass
Casting glass is a very complicated process although it is a simple idea. Idealy, solid glass will melt inside of a kiln and flow into the empty space where our wax used to be in order to take on all of the details of the wax. A simple terracotta flower pot (Must have a whole in the bottom) is suspended above the opening of the plaster-silica. This is all put into a temperature-controlled kiln. Different kinds of glass melt at different temperatures. Bullseye brand glass melts down at just 1500 degrees Fahrenheit. After the glass fills up the plaster-silica, the glass has to cool down slowly through a process called "annealing." If the glass cools down too fast, it will crack and break. This can take anywhere from five days to months depending on the thickness of the glass.
After the glass has gotten down to room temperature it can be removed from the kiln. The plaster-silica surrounding the glass can be removed (make sure to wear a good respirator!) There is one final step. We have to remove the extra glass in the space where the glass entered the plaster-silica casing. There are studios that have the equipment for this process, called "cold-working," but essentially we use diamond tipped saws and grinders to remove the extra glass and bring the glass back to a polish.
Although this process is difficult and time-consuming, I hope that it can help others to consider the uses for 3D printing together with more traditional craft practices.