https://v.qq.com/x/page/z0809ivflqi.html?spm=a2h0c.8166622.PhoneSokuUgc_3.dtitle

Spirit Slates Magnetic (Invisible Magnet)

These are terrific! In fact, we believe they are the finest set of magnetic locking slates you can see. The Spirit Slates have proven to be an extremely popular and versatile prop over the ages for stage performers, mentalists, and parlor prestidigitators.

These Spirit Slates give you a hands-free, no nonsense method of revealing mysterious writing. The flap lies perfectly flat and is invisible even under the most difficult of performing conditions. The Slates may even be handed out for close examination of the writing. They will see nothing suspicious. Nothing!

The performer presents two chalkboard slates and shows them blank on both sides. Placing a small piece of chalk between the wooden slates, he rubber bands them together. When the slates are reopened, the name of a selected card or writing on a burned billet has magically appeared on the slates. Spooooooky!

Also features:

Manufactured of the highest caliber woods!
Special permanent paint!
Larger for a better view for larger audiences!
Perfect fitting flap mechanism.
Dimensions Approximately (28cm x 19.5cm)

Comes complete with 2 Spirit Slates and instruction sheet.

Demo: https://youtu.be/m3FM-uoi4bU