Degassing, or vacuuming, is the removal of bubbles and dissolved gasses in silicone using a vacuum chamber and pump. Vacuuming must be done for all silicones being used to make toys, even those that do not need to be vacuumed to make molds such as Dragon Skin 10NV. Vacuuming does two very important things:

1. Larger bubbles from mixing are popped during the vacuuming process. These are the ones that low viscosity silicones like Dragon Skin 10NV are able to eliminate without the need for a vacuum.
2. Pulls much of the dissolved gas out of the silicone, driving it below equilibrium. The silicone will then want to absorb gas to get back to equilibrium, and one of the sources it will scavenge gas from are tiny micro bubbles created during pouring that are too small to rise to the surface or have become stuck on features in the mold.

There are some resources that have floated around suggesting degassing is not necessary and small bubbles are fine. This should be strongly discouraged for any product being sold, as bubbles often congregate near the surface of the toy where they can tear open to become pits that harbor pathogens. Additionally, bubbles in a toy more often than not elicit a strong negative reaction from customers, resulting in CS issues, chargebacks, and damage to the reputation of the indie novelty industry as a whole.

Non degassed vs degassed silicone cast in EcoFlex 00-30

Amavidi: Beginner's Guide to a Vacuum Chamber

Degas Steps 💚

Smooth-On has more specific instructions for degassing for each material they sell (check TBs) but a general series of steps is:

1. Mix silicone and pigments in a container
2. Remove all stirring utensils and load container in vacuum chamber
3. Vacuum until a head of foam appears and then breaks
4. Start time for 1 minute and continue vacuuming
5. When timer goes off stop vacuum and remove silicone, which is now ready to pour

During vacuuming the silicone will bubble up as a foam and may try to overflow the container. How much the silicone bubbles up depends on how fast it is degassed, how many bubbles were mixed in during the process, and how far along the silicone is into its pot life before degassing was started. Increasing any of these increases the loft of the foam. It is also material dependent, with Near Clear 00-31 having a loft of up to several times its volume. If the foam is about to overflow the container, you can simply switch off the pump, close the valves, and wait for the foam to break. If you are using a rotary vane pump (most of the ones with oil in them are this style) you MUST close both valves on the chamber so the vacuum does not pull the oil out of the pump and squirt it into your vacuum chamber. After the foam breaks you can open the pump side valve and resume pumping.

But what if you have a smaller vacuum chamber and/or smaller cups? The following alternative vacuuming method can increase percent fill of the container for Ecoflex 00-20, 00-30, and 00-50 to about 90%:

1. Dispense and mix part A silicone with needed pigments in a container (leave enough room for part B)
2. Remove all stirring utensils and load container in vacuum chamber
3. Vacuum until a head of foam appears and then breaks
4. Start time for 1 minute and continue vacuuming
5. When timer goes off stop the vacuum and remove silicone
6. Dispense and mix (thoroughly) part B silicone into the vacuumed and pigmented part A
7. After repeating steps 2 to 5, your silicone is now ready to pour

Please note that this method is not recommended for beginners who are uncomfortable with pouring silicone as it contains nearly double the steps of the first method listed.