Archive | Slipcasting

Fixing the leak (mostly)

Thanks to the now-working mold straps and some tips from fellow ceramists, my Elsie mold has gone from extremely leaky (bottom) to a more normal amount of flashing (top). I had underestimated just how much I needed to thicken the slip when working with a much larger casting.

I also discovered that I got much better results by pouring successive castings. Because I live in a pretty humid climate, my molds have to sit for considerably longer before I remove a casting. Not wanting to wear my molds out – which getting them too damp too often will do – I had been spacing my castings out over a period of days. My typical routine was to pour one casting and then let the mold sit for one or two days, then casting another. Joan at Pour Horse had suggested doing two castings in a row and then resting the mold. That is working much better.

Now if I could just find enough uninterrupted time to glaze a set. As much as I would like to have a set finished before the end of the year, scheduling tends to conspire against me during the holidays when it comes to things like underglazing. I can do a lot of tasks (like art glaze giftware or clean greenware) in small bits of time with lots of interruptions, but not underglazing. The threat of being interrupted – which seems worse that usual during this time of year – is enough to make me avoid the spray booth. Perhaps I should ask for a day of isolation for Christmas!

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Small breakthroughs

One day when my youngest son was a toddler, he decided he was too old for baths and requested a shower. I set him inside the shower stall in our master bedroom, and went to get extra towels just in case things got especially wet. I was only gone for a minute – just long enough to walk down the hall to the linen closet. When I came back I found him sitting on the floor of the shower, oblivious to the water falling on his head, with all the pieces of the drain scattered around him. In just that brief time he had taken it apart. I didn’t even know it came apart.

He is one of those people who are just seem born with an instinctive understanding of how things work. He gets this from his father, because I am most assuredly not one of those people. I often struggle with relatively simple machinery.

Which brings me to the item in the picture. That is the fastener on a mold strap. Mold straps hold the pieces of a mold tight while the slip is poured. I haven’t needed mold straps in the past because I have always dealt with molds smaller molds that could be held together with wide rubber bands. This has been a good thing, because I never could figure out how the fasteners worked. What is sad is that I have seen them used at Pour Horse. I’d even unfastened and refastened them, so I know how they are supposed to feel when they lock. I just couldn’t seem to make mine work.

I thought I could avoid dealing with them at all by simply using the same kind of large black rubber bands that I had used on the rubber master. They actually came off a set of “moon shoes” that my kids got for Christmas one year. When he first saw them, my friend Joe insisted that the shoes were the best job security he had seen in a while. Joe is a emergency room doctor. Shortly after that the shoes went missing (funny, that!), all except those useful-looking black bands.

I became skeptical though, when I had the completed mold. The rubber master tends to stick together a bit all on its own, so it doesn’t need to be cranked closed quite like the plaster one. I wasn’t sure the rubber bands were up to holding the large side pieces tightly enough.

As this picture of the first pour shows, they were not. The extra clay around the leg is where the liquid slip leaked between the pieces. (The white areas are from the mold soap that is present on the sides of the mold pieces.) This wouldn’t work. Not only does that slight gap distort the casting, but the clay between the pieces effectively glues the whole thing shut. It is almost impossible to remove a horse in this kind of situation without tearing it.

So I had to figure out the mold straps. I felt a little better when even my husband was at a loss. They looked simple enough, and he works in an engineering field. We must not have been the only ones, because in my search for a picture online of how they looked like closed, I found this online tutorial. Suddenly it all made sense, and now I have a tightly strapped mold. I thought it might be worthwhile to share the link, in case others were having similar trouble.


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