[aurizon]

Biscuit tins and aluminium foil have layers of insulation on them, the varnish of the tin and the Al2O3 oxide layer for the foil. It is true that the gap in each case is small, but when you look for 10 orders of magnitude in attenuation - a little leakage goes a long way. Silver has the unusual property in that both the metal and it's oxide are both conductors = true silver foil made of thin metallic silver will make a good wrap around Faraday bag. Even better would be true gold metal foil - note they often use gold plated shields in space uses, even though gold foil is like fly paper in space = contact welds readily, much more so than most other metals (many of which have also contact weld problems that have to be mitigated). Those Ramsey boxes are excellent, far better than many costlier, but crappier boxes, obviously made by someone who knows an ohm from a volt...

[formerly_proven]

I think the biggest issue with cookie tin cans is that they usually don't close all the way around, because the lid or the box is always slightly oval and not round (they always "stick" just in two or three spots when opening), so it looks like there's a small gap around half the circumference long - far bigger than the wavelengths in question.

Square tin can works better because those seem to usually scratch on the corners. The smallest square tin can you can find should work best. A tin can sealed with adhesive cooper tape should work pretty well even if the copper tape is isolated by the paint on the can.

[mcshicks]

I had to do some testing with ble temp sensors once we're I needed to isolate them and then put them in a freezer. They were in advertising mode so I could tell at least if I could see them with a phone. A round tin that was used for green tea from Japan was the most reliable method I was able to improvise. It fit very snug and the lid was about an inch deep.

[aurizon]

Yes, a one inch compressed gap like that is a tortuous attenuative path in it's own right...