applying 2.5% tannic acid solution to a cast iron trivet

Before this treatment the trivet was cleaned to bare iron then baked at 475F for several hours.

My vague understanding is that the tannic acid should applied with a brush, then the piece should be scrubbed to remove I'm-not-sure-what. Then that process is to be repeated in 45 mins; then repeated again several hours later.

This video is the first application of tannic acid. A 10% stock solution was diluted it 3:1 (3 parts distilled water to 1 part stock) for use.

Moving forward in an effort to extend the life of the working solution, I am going to teach myself to clean and dry the brush before putting it back in the solution.

The working solution was in a small container of hot water and the trivet was heated to 115F before the first application. The trivet dropped temp quickly.