Monthly Archives: March 2013

Parting line

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

a_partingline

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.

e_partingline

f_partingline

g_partingline

h_partingline

i_partingline

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

Filling

I’m filling in the five holes which are on the center axis of the figure. This is just parting line on the interior of the figure. Not much to look at really, but these details are for my own notes.

a_filling

b_filling

c_filling

d_filling

e_filling

f_filling

I’m depending on having made the silicone blanket thin enough to peel-back, pinch-away from, extract, the mass of these plugged holes from the narrow V-shaped crevice they are in. If not, I’m still confident that the silicone will peel off with only some amount to damage to the wax, which I will eventually pour into this mold, in which case , I’ll repair the wax by hand before making the bronze from it. No big.

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.

a_open

b_open

d_open

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,

e_open

carefully peal back the blanket,

f_open

more,

g_open

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,

j_open

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.

k_open

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