One of the questions posed to me the other day, about casting Hirst Arts molds, relates to the required time for casting the plaster elements. Sadly, the casting time for Hirst Arts is NOT zero.
However, with a little planning, you can complete one mold every six minutes.
Here's a series of photos showing the Hirst Arts casting process. In addition to the Hirst Arts molds (in green, plus one of my own molds in pink) you will need some plastic cups, water for mixing with the plaster (in the Indiana Jones popcorn bucket) and a soaking tub for your molds, complete with jet dry mixed in to the water, to break the water tension in the soaker. Obviously, you'll need some plaster. I recommend dental plaster...this is a 50 lb box of the stuff. You'll also need some paper towels and spoons.
The white molds are mine. The larger stack of green molds are more Hirst Arts molds, and next to them are four 5" and 6" drywall knives, used to scrape the top of the molds to make all of the blocks and elements level and the same size. Sometimes we have all four drywall knives going, which means more molds being cast.
This is the demolding table, with two bits cabinets that hold 60 drawers each. On the table are several Hirst Arts casting elements that have recently been removed from their molds. Paper towel has been placed on the table, to protect the table from scratches and assist in drawing out any excess moisture that may be in the elements as they are being removed from the molds.
Here's the other end of the demolding table. I use old plastic berry containers to hold some of the larger or more frequently cast plaster elements. The smaller or less frequently cast elements are placed in the bits cabinets.
I have a lot of plaster elements previously cast and waiting to be brought together. Here are more berry and ziplock containers holding additional plaster bits.
The casting table is set up at the entrance to the garage. The pictured molds have been pre-soaked in the jet dry tub (the jet dry tends to break up the bubbles that form in the plaster and helps the plaster to flow into all the crevices of the molds) and are resting on paper towels that will soak up any excess moisture and unused plaster. The table has been covered with a black garbage bag to prevent stratches from the plaster and make cleanup easier. I get a lot of neighbourhood traffic dropping by to see what i'm doing, which gives me the opportunity to catch up on the latest gossip while i'm casting.
I half-fill the plastic cup with water. I know there is a specific ratio, but i'm too lazy to measure the water and plaster precisely, and this process is pretty old-hat now so I go mostly on feel.
I slowly add the plaster to the water until the cup is nearly full, usually only a 1/2 inch from the rim, and the plaster no longer absorbs into the water.
Here's the final product, after some vigorous stirring with a spoon, plus a little plaster on my hands.
The plaster mixture should be thick enough that it has the consistency of a thin milkshake.
Now it's time to pour. Some people spoon the mixture into the molds, but again, LAZY, I just pour the plaster directly from the cup. A little bit of splashing, but not bad. As you can see, on the right, the first mold is poured, and bubbles are starting to form on top, when trapped air has risen to the surface.
Nearly done the pour on the second mold.
And here are the first set of six molds, poured. The next step is vibrating the molds, so that any unreleased air bubbles can be released. I'll try to get to the next steps in a day or so.