Archive | Materials and supplies


Although I have been caught up in the busy Christmas season, I haven’t forgotten little Imp. I am anxiously awaiting the delivery – hopefully any day now – of a fresh batch of rubber. I know the UPS man is ready to stop seeing my hopeful face peek out the door each time he has to make a delivery on our road, but maybe that’s because I’m always holding on to my psycho, brown-truck-hating dog when I do it!

I am reminding myself to be patient. Even if it arrived today it would still need to sit for a day or two. The components have to be at room temperature, or they don’t cure properly. I found that out the hard way last year! Uncurable rubber never really comes off, either, so it’s a good way to lose whatever it was poured over.

This mold has already lost one dried-out red band and is about to lose the other.

I am also waiting for a shipment of more mold bands. Some moldmakers use mold straps, but since most of my molds are quite small I use the rubber bands. They have the advantage of being cheap to buy in quantity and they are quick to take on and off. The downside is that the environment in the studio eventually dries them out. (The air in the studio dries everything out. After ten years I am now a connoisseur of hand lotions.) Usually they all give out around the same time, so one day I open the cabinet and find them all curled up around the molds.

That’s usually when I got hunting in my son’s things, because there are always a few up there. Long, fat rubber bands are really tempting to small boys. And it is only fair; I do filch his Legos. I didn’t find enough, though, so that’s one more shipment I’m hoping will arrive.

To bad Emma isn’t more welcoming of the delivery guy, so that he actually wants to bring the boxes here!

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Pouring the first side

I finally have Imp all clayed up. I’ve checked to make sure I haven’t missed any undercuts and that I’ve followed my mold lines faithfully. You can see I’ve cut in natches – the indented circles around the outside of the clay. Those create keys so the mold pieces don’t slip during use. At this point he’s all ready for me to pour the first side of the rubber mold.

These are the essential tools for rubber mold-making. No matter how well I mix my rubber, what’s left on the rim of the bowl and the spatula never cures. (And what does cure never comes off!) So I stock up on throw-away food containers and rubber spatulas at the local dollar store.

I use a polyurethane rubber that comes in two parts which have to be mixed in a 4:1 ratio. Normally I would do this mixing outside – instead of on my dinner table – since I dislike the smell of the rubber as it cures. Unfortunately for me it’s only 37° outside, which is too cold for the catalyst to work properly. (I had to learn this the hard way a few years ago. You end up with something that looks and feels a bit like school paste, only it never dries.)

Here I’ve just added the catalyst, which is a golden brown color. Once cured, the rubber is translucent amber.

I start by pouring a small amount of rubber and then tipping the mold around so the rubber flows around the original. What I want to do is make sure no air bubbles get trapped in the detail of the original.

In this picture I have moved the rubber around enough that the entire design area has been covered with a thin layer that is relatively bubble-free. Now I can safely pour the remaining rubber into my Lego mold box.

The original is still almost visible there inside the translucent rubber. The challenge at this point is to come back in an hour or so and add the marbles to key the back of the mold. I often forget until it is too late and the rubber has cured enough that the marbles won’t work. I am setting the timer this time, so maybe I won’t have to cut any keys.

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