Trilobe planters

In Incense holders as glaze tests, I showed my first attempt at a die for a hollow extrusion, and why it failed. Here I’ll introduce my second attempt at a die for the same hollow shape.

I showed this cookie cutter for cutting the shape of the outside of the extrusion out of a slab.

Here are the two parts of die. The inner part is intended to be held by a bolt. The notches in the inner circle of the outer die are intended to hold the ends of the spider that support the bolt. Both dies are tapered so that the clay will be wedged together as the clay passes through.

Here is the inner die mounted on the spider, viewed from the side that would be on the bottom of the extruder.

Here is the die in the extruder. You might notice that the spider is not resting in the notches intended for it. That is because the spider tapers in a bit at the end that sits on the die, and I did not measure it accurately, so the notches were too far from the center. The extruder is not very clean, because the high school students always forget to remove the excess clay when they are done. It also helps to put a rag between the clay and the piston, so that the sides are wiped down as the clay is extruded.

I made 5 small planters out of the trilobe extrusion, with the hollow tube drying overnight before being sliced.  The tube dried very fast and slumped a bit on the board it was drying on, losing the 6-fold symmetry. By the time I was shaping the 5th planter, the tube was getting a bit too dry to work with easily. I think that in future I would try slicing the clay while still fairly wet, and letting it dry to leather hard as vertical tubes, rather than as a horizontal tube.

For the glazing, the bottom of every planter had the stamps painted with black, then the excess wiped off, before any other glazing was done. Two of the pots were dipped (the brown one in temoku gold and the candy-red one in candy red)—the other three were hand-painted with commercial glazes.  All the glazes are cone-6 glazes.

All the pots are about 60mm–65mm across (measuring the highest point when lying the planter on its side).  They have two tubes (a long one for the planter body and a short one for the planter foot) joined by a slab that has a couple of holes punched in it. The slab was fresh-rolled while the tube had dried overnight, so there was some difference in the size—this resulted in a bump rather like a joint in bamboo, so I decided that it was a feature, not a bug. I carved notches in the feet, so that each planter has three separate feet.

The planters did vary in height, depending on the lengths of the tubes.  Here they are from shortest to tallest:

Yellow planter

The yelllow planter is 66mm–69mm high. The glaze is a commercial “China yellow” glaze applied with a brush in two layers. Getting a uniform coat was difficult, and some bubbles formed in the glaze.

The bottom was painted with 1 layer of commercial “marigold” glaze. The black glaze in the stamps is clearly visible.

Brown planter

The brown planter is 68mm–72mm high. The surface was brushed with steel brush before the bisque firing, making a rough surface that held the glaze well. Some of the roughness can still be felt after the glazing.

The brown planter was dipped in temoku gold glaze, using a piece of wire through the hole in the center to hold the pot. This side of the pot came out somewhat lighter and more speckled than the side shown in the previous picture.

The black in the stamped portions is not really visible with the darkness of the temoku gold.

Candy red planter

The candy-red planter (dipped once in candy red glaze) was the one that deviated most from being vertical, with the top varying from 78mm–88mm high. I haven’t decided yet whether this is a problem or a feature. Most of the variation is in the tube that makes up the foot of the planter, but there is some curvature to the top tube also.

This view of the planter on its side shows some of the curvature.

The inside of the pot is fully coated, but the candy-red glaze is nearly clear in places. This seems to be a common problem with this glaze.

The foot shows considerable distortion of the trilobe extrusion, because of the tube getting a little too dry while lying on its side. Again, I’m not sure whether I prefer a more regular “machine-made” extrusion look or this rather funky “handmade by incompetents” look. Perhaps there is some middle ground to look for.

Cherry red planter

The cherry red glaze came out as a really bold red—much better than the almost transparent candy red. The planter is 86mm–89mm talll, but rocks a little on its base.

The inside of the planter is glazed 2cm–3cm down, so that the bare clay will not show (much) when the planter is filled with soil.

The bottom of the cherry-red pot was painted with “cinnamon gloss”, which seems to make a more uniform brown than the temoku gold glaze. (I like the speckling of the temoku gold for this application, but it is nice to know that a more uniform brown is available.)

Mist blue planter

The mist-blue planter varies from 92mm to 97mm tall, but has less lean or curvature that the candy-red one. The glaze flowed terribly on this one, so I will not use it again, even though I like the color.

The bottom right foot here shows where the glaze bubbled and flowed onto the kiln shelf—something you really don’t want to have happen with a glaze!

Looking down from the top, you can see a little cracking between the slab and the sides—it was difficult to apply pressure for the joining that deep into a narrow tube. I think that there is sufficient strength, because the slab and the tubes are well joined on the outer surfaces, but I’ll have to think of a technique for making smoother joins on the inside.

The foot of the mist-blue planter was painted with purple crystal, which seems to result in a rather unpleasant mix of purple and green colors—so this pot has two glazes that I don’t want to use again. You can also see two places on the foot where the outer mist-blue glaze flowed onto the kiln shelf, even though I had left at least 3mm unglazed as specified.

So my first real attempt at using hollow extrusions was not a total disaster, though I clearly have to improve my technique a lot. If I get into the pottery class in the fall, I’ll play with this extruder die some more, as well as practicing throwing.  At least with the extruder my wall thicknesses are a fairly uniform 6mm–7mm, unlike the very thick walls of my thrown pots.

I’ll probably plant some small succulents in these pots, then give them all away.