1:72 SCALE THREE PART MOLDTo avoid sculpting in a flat surface or separate limbs from the human figure before reproducing them, I developed my own 3 part mold system. I made my first 3 part mold attempts exactly one year ago, simultaneous with my first sculpting attempts. Because sculpting and casting go hand in hand and the one is always influencing the other.
Remarkable fact: last year I could find no information on molding and casting 1:72 figures at all: not on the internet (only for larger scales) and not even in this Forum (which core subject is the production, painting and modeling in the 1:72 scale so why is the whole chapter of molding and casting absent?).
With the help of many forum members of whom BB, Phersu and Kostis have to be mentioned in particular I came to a way of molding and casting that is far from professional but is sufficient for what I need.
First a temporary central mold is made:
2 component silicone compound putty can be used for that like Sillyputty...
...but a much cheaper mix of silicone kit, baby powder and sunflower oil will do too:
It will be cured within 30 to 90 minutes.
For boxing the molding rubber, pieces of hardboard are fixed with hot glue. Any desired box size can be achieved:
But its difficult to get all box walls straight and more difficult to reach the bottom for making the clay bed.
Thats much more easy with the use of lego bricks since these can be build up in hight during a secondary phase...
...though with these the variations in boxing size are limited.
Most difficult part of molding a 1:72 scale figure is making the temporary clay bed. Water based very fine clay can be used:
Question: Does anybody know another product instead of river clay / waterbased clay? I tried several artificial clays but one was too elastic and the other one was too sticky so almost impossible to remove from model and mold afterwards.
A rough shape of the model figure is prepared into the bed of clay:
The model figure including its temporary central mold is pressed into the clay:
The clay bed is sculpted into the desired molding line.
Most difficult of all is to press the clay carefully back towards the model figure without leaving gaps and without leaving traces of clay on the figure's upper halve.
Two or more fixing holes are pressed into the clay with a wetted brush back end:
The temporary clay bed is ready now. If we wait too long the clay dries and cracks which creates gaps between model figure and clay bed:
So better pour the mold before the clay is dry. For that, a hardboard or plexiglass box has to be build around the clay bed or (like here) the lego walls have to be build up.
Many two component silicone rubbers are available:
- soft (for making single part molds)
- hard (for large or thin molds)
- colored (easy when cutting air duct canals afterwards, its difficult to see or photograph in white or translucent rubber)
- translucent (to trace back your model inside a single part mold)
- fast curing (keep the creative process going)
- slow curing (longer pot life and necessary for hard, stiff molds
For my three part molds I use medium soft rubber. And with changing the ratio 1:1 into 5:4 or 4:5 most silicone rubbers can be stiffened or softened. Like this one used by professional model casters, I got it from Hagen Miniatures:
Or the next one, from an American company specialized in special effect movie make up and Halloween masks called Smooth-On.
They sell a translucent version too:
Before mixing and pouring the silicone rubber into the box, the central temporary silicone mold has to be covered in vaseline. So the fresh fluid rubber does not adhere to it. Also the inside walls of the box are covered in vaseline to make unboxing and cleaning the lego bricks more easy after curing.
The model figure itself is not covered with any sort of parting agent since that creates loss of detail. The clay bed can be covered in vaseline or oil but its not important.
To prevent air bubbles get stuck in the fluid rubber, pour around the model figure first, if possible into the lowest part of the clay bed, so air is pushed up from the bottom and does not get trapped around the figure. Brushing the first bit of rubber directly onto the model figure and pouring in the bulk of it afterwards will help a lot. But be careful not to damage the clay bed with a hard brush.
After curing in about 30 minutes, and unboxing, the first outer mold halve looks like this (here a translucent example from a hardboard box):
The clay bed can be removed but the figure should stay into the central and first outer mold. As soon as its getting out of the outer mold, its very difficult to get it in again without changing position and shape.
Water and brush may be needed to remove all traces of clay:
Now the lower mold halve has to be boxed again. Both lower silicone mold as the central mold have to be covered in vaseline again to prevent them from adhering to the top halve.
After pouring the second outer mold and trying to prevent air bubbles from getting stuck down and around the figure again...
...it can be unboxed after curing is ready in about 30 minutes...
...and thus comes out the original sculpted model figure in its 3 part silicone mold:
When removing the model figure from its three molds, there is a small, fragile central mold of poor quality:
It should not only be replaced because of its quality but also because its round shape prevents it from finding its exact position when placed inside both outer molds again:
For that reason, the central mold has to be fixed to a fixing block:
To achieve that, a square hole in the shape of a fixing block is cut all the way from the central mold to the outside of the outer molds, enabling it to be casted by pouring fresh silicone rubber in:
Now both outer mold halves are covered in vaseline or parting oil:
The original model figure is placed inside without the central mold:
After closing a square hole is visible and turned upwards:
Enforced with hardboard plates to equal the pressure of the rubbers:
Fresh silicone rubber is poured inside to create the central mold. Air bubbles getting trapped inside can be prevented by cutting an air duct canal, by shaking the mold after pouring in the fluid rubber or by moving a pin with a rounded head inside the hole and destroy air bubbles and let them move upwards to escape. Careful with this last way: when the pin removes the vaseline inside, the central mold will adhere to the outer ones.
At the bottom of the mold the air duct canal is visible, silicone rubber leaking out but it helps the air to escape and the rubber to pour in.
After curing:
Removing the master model figure:
To be continued....
Next time: casting a 1:72 scale resin figure in a three part mold.