Tag Archives: cyclops

Silicone back

I’m doing the second side, the back side, of silicone mold. This repeats the steps done for the first, front, side. Of course, the mold is turned-over now. Apply a liberal amount of release to all the surfaces of the two halves, the one with the model sitting in the silicone of the front side, and the other, back side plaster. Where silicone will meet silicone there must be a barrier of release or else the two halves will bond permanently. It is surprisingly easy to neglect this for some reason, when one is pre-occupied with so many details to consider. I apply paste wax (Briwax) to the plaster, several coats, and a spray type release I’ve mentioned before, which is hydrocarbons in ether, or something. Works fantastic. I’ll say it again: APPLY A LIBERAL AMOUNT OF RELEASE TO ALL SURFACES. If you can’t remember clearly applying release, then do it again.

Assemble the plasters, strap it together and again, cover the feet/pour spouts area, sealing it tightly so there will be no leaks.

a_siliconeback

And that box mold I’m doing on the side? I added some pour spouts there too, and applied release. I’ll pour the second half right on top of the first, with whatever’s left over in the bucket from the big mold.

Here’s the mold, with the silicone poured in. Like before, there are vent holes at the high spots which let air escape the mold as the silicone fills it. The clay plugs the holes when the silicone oozes out. I have again mixed up 250% of the volume of the clay blanket removed in the last step. It follows the formula: The weight of clay times 1.06 equals the volume cubic inches of the clay. The volume cubic inches times .68 equals the weight of the Mold Max 30 silicone product that I’ll need. The rational about qualities to mix up are all in the earlier post “Silicone front”. On that first side, it turns out I had a good bit of silicone material left over, even after the box mold was poured. Based on weighing the leftover amount, just doubling the volume of the blanket would have been enough. And although I know this, I’m still going to use 250% volume, to be safe. It is a large batch, as much as I can get into the vacuum tank at one time.

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Enough to fill up the box too.

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After curing for 24 hours, I open the foot-cover to see. It’s all good, but do notice that 10 grams of material has leaked into the left spout. The seal wasn’t perfect.

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Split the mold open carefully, slowly, gently.

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The mold, by chance, opened with the first side facing out. This side hasn’t seen the light before, and it’s our first look at it, but it isn’t the side we just poured. It looks good without any air gaps at the high spots – all the venting worked properly.

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I want to free the other side. I invert the whole thing and suspend it on some cups to let it, sort of, ease its own way out, for a couple of hours.

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Then I gently start to pry it away from the plaster shell…

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..until it is worked loose.

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Interesting. See the air gap there on the belly of the figure? Although there had been oozing silicone out of that vent hole before it was plugged, there must have been some subsidence of the material while it was curing, leaving that void.

o_siliconeback

I think it may be the same amount of material which found its way leaking into the foot-funnel. Or perhaps, because I forgot to seal the edges around the plaster half with the blue tape, air got into the mold and allowed the subsidence to happen. Otherwise, the clay plug should have secured vacuum to hold the silicone up. Who knows, but in this case it is easy to fix. I’ll re-assemble the mold and pour some silicone directly down the vent hole and fill the void. Since I will not apply any release to this area, the new materials will bond tightly to what’s there.

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After 24 hours I open the mold and see that the repair is good.

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Parting line

I added vents at the ends of the arms. They are cocktail straws, snipped and buried halfway in the clay bed.

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At last I’ll finalize the parting line around the piece for the mold halves. Prepare a variety of clay snakes, collect your favorite tools, and find a comfortable place to work with good lighting:

b_partingline

Also, have a good cup of coffee, and listen to Radio La 2×4 Buenos Aries. (http://www.buenosaires.gob.ar/la2x4)

The techniques I think works best is, having built up in a general way close to the piece, to now lay a line of clay along the remaining gap of about the same size as the gap or slightly larger, and simply press it gently into place with small tools.

c_partingline

This neatly fills and seals the gap, without applying pressure onto the piece which will make the clay line difficult to remove cleanly and without blemish to the piece later. The gap must seal completely.

One side done, halfway around.

d_partingline

And finished, including some keys which can help to keep the two halves in alignment. I don’t take keys too seriously like some people. I think the complexity of the plaster mother mold’s shape, is enough to keep the silicone in place, but people expect to see these in a mold so  do a little of it, for example. I think channel shaped keys like this do more to help prevent material you pour into the mold, like wax or plastic, from leaking out at the seams while it solidifies.

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Next, I’m ready to pour the silicone to form the blanket mold of the first side you see here. Exciting!

Open

I had to go snowboarding again, sun and snow perfect, clear-minded oblivion. By now the plaster shell is really dry. I stand it up and very carefully, open it by inserting some wooden wedges  and tap gently with a hammer. As soon as the suction is broken it comes apart easily. Do not pry. Be patient. I open the mold so as to reveal the first side that I worked on, that hasn’t seen daylight since the end of December. Nice, isn’t it? Face it, there is satisfaction in doing your craft right.

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b_open

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Now I’m going to remove that pretty clay blanket and reveal the model under it. I’ll use a palette knife to cut and separate the blanket from the plaster,

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carefully peal back the blanket,

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more,

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and more, until the model is revealed, but still resting in the bed of clay which is the second-side blanket. I had done some work earlier on to roughly define a parting line in clay from this first side, when it was still in the cradle, and you can see some of that in place still. The task now is to detail that parting line perfectly.

h_open

I save the clay blanket that was removed, because I can weigh it and know roughly the amount of silicone rubber I’ll need later to fill the void between where the blanket was removed and the plaster mother mold. We’re some way off from that still.

i_open
I cut back the plastic wrap with small scissors, which has been helping to protect the model from the clay blanket to the existing rough parting line,

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and tuck in the loose edges under the rough parting line. This way the plastic is still protecting the second side, you don’t need to remove the model from the mold at all, to get the plastic off, and it’s usually hard to do that without harming the model anyway.

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l_open

There we are, ready to begin work on the final parting line. I’ll point out that the outlines will be pretty simple, but the holes through the middle of the body must be handled somehow and even though the silicone rubber material is very forgiving about undercuts and such, I’ll need to proceed with deliberation and reason.

m_open

Back plaster

I boxed up the mold, preparing to pour the plaster for the back side. I just build this quickly using foam-core, hot glue, and tape, lots of tape. I seal the inner seam of the box with clay where it meets the front side plaster so there is no leaking out of the new plaster. I line the inner side of the box with packing tape to release the plaster. I added the sprue and vents for the silicone to eventually pour into, in the form of cardboard tubes and soda and cocktail straws, but that step is still a way off (the clay under the plaster will be removed and replaced with poured-in silicone, forming an inner blanket which is supported by the solid plaster outer mold). It’s a lot of details with not much to picture.

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Mix the plaster, something I’m not showing you, pour it on and shape it up. You can see some markings above which I use to estimate the thickness I want from the plaster.

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I’ll let this dry a few days, take away the box and smooth it out some more.

It is a relief to be at this point. I’m maybe halfway done, but some of the most critical planning and preparation steps are complete now, and if I’ve done this correctly, most of what follows will be clean straight-forward work without anxiety.

Back blanket

It’s been a while. Went snowboarding in Wyoming with my brother-in-law, his wife & my remarkable niece. What fine hosts, and I had the greatest time there. I’d been to the Tetons many times in the summer to hike and climb, but this was my first time there in winter to snowboard. An excellent variety of terrain, rugged and scenic. I miss those days when I would lose myself in nature & the dissolution of the self, but after being so out of my head there and on return, I and ready to get back to work on this. The few people following this blog have told be they have in fact no complete idea what the process is here I’m illustrating; and how I can focus so much seeming effort upon it?

It is the complexity of it all which lets me lose myself in the work.

Here’s the first side again, now trimmed back from the edges to expose the plaster surface and match the extent of the first side blanket, which of course you can’t see, so it’s helpful to have pictures to refer back to. The new second plaster side will match face-to-face with the exposed plaster, creating a shell, or mother mold, within which the silicone mold is supported.

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Another clay blanket is made now for this, the back side of the model. Again, these are sheets of clay not more than 3/8th inch thick, laid on the model.

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After a rudimentary smoothing-out. This layer will become the shape of the silicone mold rubber to eventually take its place, and the second side plaster will be poured on top of it, so it must not have any undercuts to interlock with the plaster.

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The nearly final form of the blanket.

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Next, I create the sprues and vents for where the silicone will (eventually) pour in, and box it up all around (again) so the plaster can be poured on.