It is important that the coating on cast iron is subjected to a certain amount of blunt force to determine the strength of the coating - this method is called an impact test. The process of impact testing is simple, requires no technical equipment or materials, and you don't need to be a professional. The materials required for the impact test are 350 grams of steel balls, a length of 150 centimeters of PVC pipe, a piece of double-layer cardboard and a piece of ceramic-coated cast iron cookware. The diameter of the PVC pipe should be large enough to allow the ball to pass through without resistance and with little space around it.
Before you start testing, you need to know if the cooker you're testing has what's known as a drop circle. Drip circles are grooves in the bottom of a cast iron pan or pan that cause the coating to be ineffective. Grooves are usually caused by impressions of the manufacturer's logo left in the mold. It is important not to drop the ball directly on the drop circle, as this is a weak point in the coating that is more likely to crack and produce inaccurate results.
Now that you know the equipment you need, let's step into the coating adhesion testing procedure:
Lay the cast iron product (bottom up) on a double layer of cardboard on a hard floor.
Drop the steel ball from the top of the PVC pipe directly onto the flat outer bottom of the item, 1 point around the drip circle. Make sure the ball doesn't hit items on curved edges or side walls, as the coating is weaker in these areas.
After impact, inspect the contact points, looking for any chips, dents, scratches, peeling, or other damage to the cookware item's surface enamel. Small dimples in the enamel are acceptable. However, if the enamel falls off like an eggshell, cuts away at places other than the point of contact, or shows damage, the item fails the test.
Repeat the test at 3 different points around the drop circle.
Impact testing was also performed on the inner surface of the cast iron to evaluate coating adhesion. The test internally involves the same procedure, but you need to drop the same steel ball from a lower height of about 70cm. Again, be sure to land the ball on the 4 points around the drop circle for accurate results. As with the test exterior, you'll likely find at least one small circular dent or scratch in the coating, but it should be round, regular, and present only at the point of impact.
