This is my first post here, nice to meet you all.
I have a question about some result of fired colored porcelain. I am making some unglazed porcelain objects, with the goal of having a very matte finish. Now I have made a test with porcelain colored with a black stain, I have added 4 % to the slip. The stain is based on Co-Fe-Cr, it's standard stain I purchased at a ceramic supplier, the same goes for the slip. What I did:
- First did a bisque fire (electric kiln) until 950 degree Celsius (1742 degrees Fahrenheit)
- I removed the objects and finished them (sanding) to a more smooth finish
- In the kiln again, fired until 1230 degree Celsius (2246 degrees Fahrenheit)
The result is a matte looking porcelain, but it has some unwanted glossy spots on the surface (see attached photos). I do not understand why this is happening. Maybe somebody has an idea what could be the cause of this?
Thank you in advance.
greetings, Patrick Hartog