Outdoor finial material considerations
These fantastic oriental style ceramic finials I made for a Japanese bridge in the garden. In 2014 I made plaster pieces, but they were unsatisfactory. What material would endure outdoors for these ornaments?
Recently, after a trip to Japan, I realized that if I could make the finials using ceramics instead of another material they would basically last forever. The following photos show the process I followed to make the Japanese finial.
Description of mould Making Process
Firstly I designed the oriental style finial in CAD from which a 3D printer STL file was saved. After printing the STL file I had a 3D model from which I could make the plaster mould. The mould was made using plaster of Paris in four sections.
Once the mould was finished it was assembled and had porcelain slip poured in. After about half an hour the plaster absorbed some moisture from the slip causing it to set and shrink slightly. The remaining slip was then poured from the mould leaving a 3mm shell inside. The mould was carefully disassembled and the greenware finial was removed. This process was repeated twelve times.
After cleaning up the greenware they were bisqued in the kiln to 980 degrees. The following day, after cooling down, they were glazed with Iron Lustre, Vintage Gold and Art Deco Green. They were then fired to 1220 degrees. The finish was spectacular. They looked fantastic.
The finials were then attached to the Japanese bridge as shown in this post.
Photos of the mould making process
Here the 3D printed model of the oriental finial has been divided into four quadrants and flanges with alignment keys have been set on one quadrant.
This process was repeated for the other three quadrants.
This photo shows the completed four plaster mould sections. These will now be joined together in preparation for casting.
Here the porcelain slip has been poured into the mould. It is just slightly overfilled. After about 20 minutes the level drops slightly as the plaster absorbs the water from the slip. Just top it up a bit to get it full again.
After the slip is poured from the mould you are left with the shell of the finial inside. It shrinks slightly due to the water absorption but this makes it very easy to remove.
The process was repeated twelve times.
Here the first mould section has been removed revealing the casting of the finial. The other sections are carefully separated and the greenware finial is removed from the mould.
Here are the twelve finials awaiting cleaning up before being bisqued.
After bisque the finials are glazed prior to final firing.
After being fired to 1220 degrees the finials have come out of the kiln looking brilliant!
When the finials were cast in the mould there was a little shrinkage as the water evaporated from the slip. Again, after the bisque firing they shrank a little more. There was even more shrinkage after the final firing. Doing a rough calculation comparing the original 3D printed model to the completed ceramic finial there was about a 15% shrinkage as shown in the photo below.
