A well-known challenge for DIYers and homebrewers who want to work with ferrite components is that most of the time, these components do not carry markings or labels on the ferrites themselves, and the type of ferrite is usually critical for a particular use.
There are lots of articles describing how to use a grid-dip meter or VNA to determine what kind of ferrite is being examined when they are encountered at a flea market or are otherwise of unknown providence. Unfortunately, these steps are finicky and require one to carry a bunch of test equipment around with them (and know how to use it).
A simpler, more direct solution is to mark the ferrites when you obtain them in a way that is both easy to read and difficult to remove. Unfortunately, most ferrites are difficult to mark with conventional pens or markers since they are usually a mix of ferrite or iron power and ceramic, and are hard, brittle, and non-porous.
Fortunately, my wife is a potter, and glazed pottery and porcelain has many of the same issues with respect to applying markings to it, but people have come up with solutions to the problem:
This marker is white, so the markings stand out well against a black background, and it actually uses paint to mark the item, so the markings are both durable and difficult to remove.
