The model is very simple, and the spare is incorporated. However, its "mushroom" shape requires the making of a 2-parts mould.
The mould of the coresponding cylindrical box is already made, but I want to mold the lid four casting and and firing them together, this will perhaps avoid the warping, probable at High Temperature ...
There are two ways of proceeding: either we lay the model on the edge and “bury it” up to its median (horizontal) line, and by pouring a first leveling plaster. Again we proceed to the molding itself, pouring plaster on top. Then we turn over the first part and we mold its complement ( second part of the mould). This gives a rectangular mould on the outside. This requires three plaster fabrications for a clean mould (the buried part poured to the center line + the first half of the mold + the second half) ...
Or, we put the model on its base, (with its vertical center line), we cut a plate of setting in range, and we mold a first half; then, the vis-à-vis is molded after removing the scope. The formwork being this time, cylindrical. This requires two fabrications of plaster.
I chose this second version, and I show you the preparatory work:
Drawing on graph paper of the profile of the model and therefore of the cutout of the profile bat. I always take advantage of the plaster preparation to make additional bats with different thicknesses , on a glass window, for using in different ways. Here, a thin bat will be cut with a precision scroll saw to "frame" the model.
You have to take into account the thickness of the cut and saw a little larger, it is easier to refine the measurements with a file, than to run out of material. Diagonal sawing (when the plate is thicker) allows better adjustment to the shape of the model.
Then we proceed to the installation for the molding: we put the model (two dots of UHU glue) in the center of a plasterboard cut in a circle, leaving about 3 or 4 cm around the model, (this will be the thickness walls of the mold). The model is placed on its spare, this is the slip pouring side.(Check the flatness and verticality of the plate)
Place the profile bat carefully along the center line of the model, and seal it on the back with a little clay. The surface and the volume which will be embedded in the plaster for the first part of the mold are thus left well clear.
Then soap carefully with a brush (slightly diluted black soap) three times, each layer after the previous one is dry. All surfaces (spacer, model and profile bat) must be well soaped, otherwise the plaster will stay glued to the model. Be careful that the soap is not too thick and does not leave traces, because the plaster reproduces the details finely! You can finish with a finer brush, just damp to "hollow out" the corners.
A rhodoid cottling sheet is then wrapped around the edifice and it is immobilized with an elastic band or a string. The plaster pouring level is marked with a felt-tip pen, 3 or 4 cm above the model (this will be the bottom of the mould).
The smallest gap is filled with clay so that the plaster does not leak.
Then make the plaster and pour it.
When the plaster has set well, has cooled, we can undo the setting, that is to say carefully remove the spacing bat, freeing the space that will be molded in the second part of the mold. With a small coin, dig two holes on either side of the model, as "natches" or registration points. The other half of the mold will come to fill them, and this will form a good mark for the closing of the two parts of the mold.
Once the marks have been dug out, the new exposed parts are carefully soaped :3 layers or nothing!
We redo the plaster and we pour again, stopping just at the same level as the first block.
Once the plaster is well set, do not try to open your mold right away, it is still waterlogged. It is better to wait until the next day, and with a simple piece of metal, it will be easy to open the two-part mold, and carefully take out your model.
Now clean the mould, dissolve the soap (wet sponge), and champfer the sharp exterior edges, to protect the mould against shocks and facilitate gripping.
And patiently wait for complete drying before making the first slipcasting ... in ten days!