OK, so after casting ten of each of the fieldstone bridge and castle tower molds, I noticed that as careful as I had tried to be, I still had a few pieces with minor bubble problems. Nothing to be concerned about, I hope, but it still annoys me that I could be that careful and still have bubbles. Also I was getting tired of the mess.
The way Hirst suggests that you fill your molds is to pour a thin stream of plaster on the edge of the mold cavity (usually between a couple of cavities) and allow the plaster to slowly flow down the side and then to fill in the entire cavity from the bottom up. Then, without stopping the stream, move to another edge and do the same until all the cavities are filled. This will end up with some extra plaster on the top of the mold, but you will scrape that off after it sets a bit so that you end up with a completely flat “top” (which is usually actually the bottom) of the molded piece. You do end up “wasting” some plaster since you are pretty much pouring plaster all over the mold until it overflows each cavity and with the trails of the flow as you move it around, you end up with pretty much the whole mold covered in a puddle of plaster. When you scrape the excess plaster off, you leave a huge puddle on your work surface. I have been scooping that up and tossing it into one of my big column molds so that it isn’t wasted, and as a result I’m getting close to having 30 columns now, almost enough to do a replica of the Parthenon…
But the thing is, getting that smooth, perfect, thin flow of plaster going is hard enough in the first place. Keeping it going four an entire pour is extremely difficult. The dudes on the instruction videos make it seem so simple, and I suppose it is if you pour molds for several hours every day like they probably do. But in my case I get burps and blops and surges and times when the plaster curls under the rim of my plastic cup and starts to crawl down the cup on my fingers, dripping all over creation….
So… last night, after laying out all the items and seeing that some of them had bubbles in spite of my best efforts, and looking around my room and seeing all the excess plaster all over the place, I decided there had to be a better way.
It turns out that a long time ago I bought a fairly expensive guitar humidifier device. It is a little plastic doodad with a sponge inside and you fill the sponge up with water and place the device between your guitar strings so that it hangs into the guitar’s body cavity. There it will slowly moisturize the guitar. To fill the device it came with a syringe about the size of my index finger and about as big around as my thumb. The syringe has an open plastic nozzle and it looked to me like it would be perfect for plaster.
But what about my guitar? Well, I don’t use that humidifier anymore since one of my guitar expert friends informed me that they are the least effective humidifiers (in spite of being by far the most expensive I saw), and I now use a plastic circular humidifier which fits snugly in the guitar hole and essentially seals in the moisture so that it has nowhere to go but into the guitar body. So the syringe was just laying around…
So this morning I whipped up a batch of dental plaster and used the syringe to fill up the cavities.
OMG! This is so NICE! And NEAT! I have almost total control of where the plaster goes, the speed it flows and there is no trail of plaster as I move from cavity to cavity. I fill up just what is needed with just enough excess so that I can offset the settling that occurs with the dental plaster I’m using, and I ended up with no more than a teaspoon or so of excess plaster, which I put into the column mold.
But the proof of the experiment isn’t whether it is neat, it’s whether it defeated the bubble problem.
It’s only one cast, but every single item, even the most intricate and tiny one which was the most difficult to fill with the “pour it from a cup” method, all came out downright perfect.
I did have to use a bit of extra water to clean out the plaster from inside the syringe before it cured, but that’s not any problem.
The one thing I wish is that the syringe had a longer and curved nozzle. And guess what? They sell exactly that at pharmacies. So I’m going to pick up a few today.
I’m quite pleased with the results of this little experiment. Neater, faster, virtually no cleanup and most importantly… NO BUBBLES!!