The next step is baking the cups. We learned by trial and error that this part of the process is very delicate. It took us several rounds to develop a little sense of control over the process. We bought an old used kiln on an online market place for about €150. The kiln broke down at the very first baking session and we had to replace the thermostat. A good thing in the end, because it gave us the opportunity to learn more about the electronics under the hood. In the very likely case that you don’t have a kiln yourself, it is recommended to search for ceramics studios or workshops around you. In many cases they offer possibilities to bake the clay cups for you at a fair price. Each cup needs two baking sessions. The first session is to bake the clay (biscuit baking) and the second one is to bake the glaze.
The first baking session is called biscuit baking. Basically it is baking the clay without the glaze. Our kiln doesn’t have baking programme settings or the possibility to set the temperature. We use a high temperature thermometer to measure the temperature in the kiln. We found several baking schemes online that we experimented with. Here are links to two of them: the first one (Dutch) and the second one. We used 1050°C (1922°F) as the maximum temperature.
The glazing was the most problematic part. In our first experiments we used ready-made glazes from the brand Botz bought at the online ceramics shop. To apply the glaze we used glaze brushes. We made several attempts with different kinds of the same brand. In all cases the glaze cracked after the baking session. We heard continuous cracking sounds and when pouring coffee in the cups this cracking accelerated (see the photo below). In our latest attempts we used a combination of glaze powder, pehatine and water to make a glaze mixture. This worked for us and the glaze didn’t crack afterwards. We finally were able to drink a cup of coffee with our ceramic cups.
The results are still not perfect. The glaze doesn’t seem to be spread equally over the cup. Dipping the cup in a glaze bath or air brushing the glaze could possibly solve this problem.
Example of a cup with cracked glaze.
Glazed examples that worked out better.