Many of the mold making and casting materials tend to trap air which shows as bubbles in the molds and casts. Special techniques and equipment are required to remove the air and allow perfect castings.

Every mold maker and casting artist worth his name is familiar with the various processes and techniques involved in these crafts. The regular procedures like cleaning, sealing, applying the release agent and making the mold box are followed to the letter. Similarly, the pot time, cure time and other processes are accorded due importance in the course of things. The artist will also pay attention to proper demolding, finishing and the like.

However, many tend to overlook the need to degas the mold making and casting materials. And this is where equipment like vacuum chamber, pressure pot and vibrating table enter the picture.

The whys and wherefores

When working with materials like resins and rubbers, artists soon realize, much to their detriment, that the molds and casts tend to have air bubbles on the surface after curing. These are very tiny, and yet, spoil the appearance - and sometimes even the utility – of the mold or cast.

This is usually because of the air that enters the material while it is being mixed. This air gets trapped in the form of tiny pockets which will show up after the material has been poured into the mold box or mold. At times, artists get by with techniques like mixing the materials slowly, pouring in a narrow line from the corner or even tapping the container/mold to release the trapped air.

However, they do not work all the time – especially with clear casting resins and rubbers. Hence, rather than have the artwork marred by the unsightly air bubbles, it makes sense to degas the material before using it!

How to do it?

A vibrating table is considered a simple solution for deairing materials. The vibrations lower the coefficient of friction of the material which will bring the air bubbles to the surface. These can be easily popped with a pin or toothpick. However, this is not a foolproof method by a long shot.

A pressure pot works on the principle of subjecting the material to high pressure which will squeeze the air pockets to very minute and microscopic size. This is useful for resins as they set to a rigid form. So, once the pressure is released, the air bubbles will not have the space to spring back to their original size and will stay compressed.

Then comes the king of them all – the vacuum pump with vacuum chamber! This works on the opposite principle of removing all the air and creating a vacuum inside the sealed chamber where the material has to be kept. It is apt for rubbers as they cure to a flexible form and thus the pressure pot will fail to get rid of the air bubbles permanently.

All said and done, choose the best equipment from a reliable source and get set for making perfect castings!