Silicone Pinch Test: when you pinch, twist, or pull a silicone product if it turns “white”, then it contains fillers and is therefore not safe or a good quality silicone.
It is a common misconception that the presence of white fillers in silicone kitchenware indicates that the silicone is not safe or of good quality. However, this is not necessarily true. Silicone does have fillers, but the fillers≠bad quality. To figure it out, first, we need to know how silicone is made.
1. What is silicone? how silicone is made?
2. Precipitated Silica VS Fumed Silica
a. Method of production
b. Difference Between Precipitated Silica and Fumed Silica
The last difference between fumed silica and precipitated silica is the cost. Fumed silica is more expensive than precipitated silica due to the differences in their production processes and the resulting properties of the silicone. In the rubber industry, fumed silicas are limited due to expense, mainly used as reinforcing fillers for silicone rubbers. As silicone rubber fillers, precipitated silica is an alternative to fumed silica in silicone rubber compounds by reducing cost and process in efficiencies for silicone rubber compounders.
3. The different impacts of Precipitated Silica and Fumed Silica on silicone
Silicone with Fumed silica as filler has much better tensile strength, abrasion resistance, and Elongation than Precipitated silica.
Silicone with fumed silica as a reinforcement filler can have higher transparency. Fumed silica can produce translucent or even clear, non-yellowing silicone with minimal aging effect. silicone with precipitated silica as a reinforcement filler may have low transparency.
Silicone with precipitated silica as filler will turn white when stretched or twisted, but fume silica won’t.
Silicone with fumed silica as filler will have better quality than precipitated silica.
Why silicone with precipitated silica as the filler will turn white when pinched or twisted but fumed silica won’t?
4. Misconceptions on silicone pinch test
One common misconception about the silicone pinch test is that if silicone turns white, it is of bad quality that is unsafe.
Use pinch test to tell if the silicone is food-grade or not. If the silicone turns white, it is not food-grade.
Take pinch test as a way to tell “food grade” or“medical grade”.
Misleading that if silicone changes to a whiteish color, then it most likely has plastic fillers.
There are professional companies that provide inspection, verification, testing, and certification services. Such as SGS,Bureau Veritas, Intertek, and TÜV SÜD. Some silicones can be certified for both medical and food uses depending on the testing they have been subjected to. Like there are different tests for “medical” certifications, and there are also different tests, and levels of certification, for food applications. The two main tests for silicone are FDA & LFGB testing.