Before leaving for Kohler, Ian laser cut plexiglass positive and negative shapes to exact dimensions for us to use in creating the models for each tile. These pieces show the high and low spots which will help us in carving the plaster models.
In order to cast the forms to make the models, the negatives needed to be as close to perfect as possible. Any imperfection in one tile will be compounded as the tiles accumulate and will throw off the installation. Here, Daniel is filing the plexiglass negatives so they are square and even.
Next, Daniel cut the forms apart so they can be pulled apart after the plaster is poured.
The wet plaster poured into the form, then scraped away, leaving us with a flat block from which to carve the tile models.
pulling apart the forms to reveal our first model blank, ready to begin carving.
Thousands of square feet of the Kohler Pottery’s casting floor surround our little studio. They cast the molds once a day, during first shift. By midday most of the pieces are out of the molds and drying. Right behind our space they cast urinals.
I don’t usually think of urinals as elegant design, but then I don’t usually see them like this.
The full length urinals remind me of the boys’ bathroom in elementary school.
Daniel cleans up after pouring the last piece of our first molds. We figured they might not work, but would hopefully give us good information and we could start troubleshooting. We stuck them in the fancy dryer they have in the factory…
…and cast them the next day. Which is crazy fast. Also notice the pressurized slip pump.
A very pleasant surprise. Both molds seem to be casting well. We’ll get these in the kiln tomorrow.
Removing the mold pieces
Carefully pulling out the finished piece
Cutting off the nubs that form at the bottom of the funnels when casting solid objects
Our first molds seem to have worked out, so it’s time to move forward on the rest of the plaster positives. For each shape Ian made a plexiglass template from which we transfer the intersection points of the design.
Then those points are connected, giving us guidelines for carving the design into the plaster.
It’s slow, fussy work.
Which is the kind of work we like.
We’ve each developed our own strategies, and our favorite tools, for getting the facets just right. Here is Daniel’s spread, including some great little steel scrapers that his grandfather, a sculptor, used to use in his own work.
And you can see where this is headed.
At least at this stage that’s how we measure it. And by that measure today was a successful day. Our first piece went through the kiln and came out looking like this. We sprayed on Kohler’s regular Toilet White glaze (not what they actually call it). It’s not what we have in mind in terms of surface treatment, but worked fine as a test.
It was in there somewhere. 2200+ degrees and back again.
We got 2 more tiles out of the kiln this afternoon, experimenting with Kohler’s Honed Black glaze. These are more of what we’re looking for on the passive solar south wall in the Core House. The matte finish catches the light much better and makes those facets pop. Stay tuned for a lengthy mold making process post later tonight.
We’ve started casting and firing this week, with very promising results, but mostly we’ve been up to our elbows in plaster, making molds. Plaster molds for slip-casting are a means to an end. They are not the final product – just another tool, really. But we love tools. And we love making them. And we’ve gotten a little obsessed.
First, we make sure our models – our plaster positives that we’re hoping to reproduce in clay – are pristine. Any nicks or air bubbles are filled with oil clay.
Coddle boards are set up around the models.
A clay wall defines the boundary of the first pour and keys (plastic buttons in concave/convex pairs that will later help register the mold pieces to each other) are set.
Sometimes the cleanup between pouring each piece can seem endless. But care at this stage pays off with mold pieces that fit together perfectly and produce a clay object that is as close to the original model as possible.
Pieces that butt together are keyed using this round sureform.
For pieces that sit atop one another you can use the plastic keys seen earlier, or simply make round indentations in the plaster. Some people use a spoon or a coin. We use a custom Ian Henderson key cutter (i.e. washer welded onto steel rod) in a cordless drill.
The cleaned up, keyed mold piece is reunited with the model.
And everything that will come into contact with the wet plaster of the next pour is covered with mold soap.
The coddles are removed as the plaster starts to set but before it is fully cured.
And the plaster is scraped away to the top edge of the model. In slip-casting the seams where mold pieces meet each other will always show up in the final product. By placing the mold seams on the corners and edges of the piece, though, they become essentially invisible.
You can see why some cleanup is required between pours. The newly poured piece is sanded and keyed.
And the whole thing is reassembled again, coddled again, soaped again. The next steps are simpler, though. The bottom piece of the mold is poured and left to cure.
We had two going at once.
Everything is reassembled and soaped in preparation for the last pour. As you can see, this part happened during respirator hour in the factory.
The second half of the plastic key pairs are set in place, as are the red plastic ferrules where the slip will enter the mold. Tapered pieces of rubber are stuck on top of the ferrules. They will later be removed, creating holes where the funnels will fit.
Ready to pour.
All four mold pieces, plus the model.
Lastly, the mold soap needs to be dissolved with vinegar and sponged off. It’s hard to see or feel with your fingers if you’ve removed all the soap – but the tongue never lies.
The finished molds wait to go into the dryer with a bunch of Kohler ware. Daniel made these two and they came out looking great. A number of people in the factory commented on how nice they are. Which is all fine and good, but the proof, you know, it’s in the pudding…
Plenty of people do it differently – and better – than us, but that’s our process. So far it’s all working out astonishingly well.
The most labor intensive model and mold we’ve tackled so far is the decagon tile. It’s the largest tile at 15″ diameter and 1″ thick and we’ve had lots of commentary from the factory associates about this one. The guys on the kiln line said it made them nervous to put it in. The pottery technician told us 3/4″ was the maximum thickness. Tom Spleth said things can start to get really tricky over a square foot. So, we have been really nervous about running this one through the process.
Here it is in progress with Ian’s favorite carving tool: a 6″ ruler.
You’ve seen this step before, but I think this is a really good looking pattern.
And the successful first cast of the decagon. It seems to be casting fine. It made it through the dryer twice without cracking or failing. We are currently waiting with white knuckles for it to come out of the kiln this afternoon. We will let you know how it went.
Sorry about that. Anyway, the decagon made it through the kiln just fine, as you can see. We have now successfully cast and fired at least one of each of our five tile shapes, which is a relief. The only thing standing between us and full-on production mode is finding the right surface treatment.
We’ve been sending a couple tests through the kiln almost every day.
As a result we’ve had to get serious about documentation. Each tile is stamped with a number so we can keep track of all of our tests and we record any information we can think of like which mold it came from, what we added to the slip, and what glaze we applied.
Meanwhile, every day we are getting new molds into production. Here are some freshly cast pieces arranged with models. These are two of my favorite surfaces – plaster and leather hard slip. I always get attached to the objects at this stage. By the time they come out of the kiln as shiny, shrunken imitations of the original, I feel that something has been lost.