Step 1: The Problems to Overcome...
In the UK, there are limits on the strength of magnets that can be sent through the post. You cannot send...
Magnetised material with a field strength of 0.418A/metre or more at a distance of 4.6 metres from the outside of the package.
I have no idea whether the magnets I used are that strong, but I had another problem because the rules also say that magnets should be sent...
... individually as magnets can damage other items they travel with, i.e. discs, tapes, etc.
The pendant I made has four magnets, so I can't follow that rule, either.
If you do post more than one magnet, it's possible to arrange them so that their fields counteract and cancel each other out, but the magnets are fixed in place in the pendant, and I arranged them to reinforce and increase each others' fields...
Step 2: The Enclosure
You need an enclosure made of steel or iron. The perfectly-sized item turned out to be a small tin of pineapple rings.
Open the tin, eat the contents and clean the tin.
Step 3: Tidy the Tin
I had help preparing this instructable - a hungry teenager.
Unfortunately, she was very hungry, and made a bit of a mess of the edges of the tin. A pair of pliers served to tidy up the torn parts.
Step 4: Card Packing
If the magnets touch the tin, then the tin also becomes magnetised, defeating the point of this project.
I cut a stack of discs from thick corrugated card (enough to fill the can), and cut a circular hole in the middle of two of them to form a "nest" for the pendant.
Step 5: Pack the Tin
Put half the solid discs in the bottom of the tin, add one with a hole, then lay in the pendant.
The second disc with a hole went in next, followed by the rest of the solid discs, pressed in firmly.
Step 6: Test
Normally, if you drop a pin within a couple of centimetres of the pendant, it sticks to the pendant.
When I dropped the pin onto the closed tin containing the pendant, it just slid off without slowing, showing that the magnetic field of the pendant was effectively contained.
Step 7: Tape, Label, Done
A layer of tape around the top of the tin both covered the sharp edges and held the lid in place.
I also added a strip of tape across the top to allow a warning about the sharp edges and the magnets.
That was it. The tin can went into a padded envelope, and the envelope went into the mail, off to a (hopefully) happy customer.