[ejolto]

Depends what the tin and shaker are made of. The tin is probably made of aluminum which has a higher skin depth than stainless steel, which I assume the shaker cups are made of. A Faraday cage of continuous surface needs walls that are thicker than the skin depth of the material the cage is made of. Since the skin depth of stainless steel is lower, the cage wall thickness can be lower while still creating an effective Faraday cage compared to an aluminum cage.

Ref skin depth of different materials at different EM frequencies:https://upload.wikimedia.org/wikipedia/commons/f/f3/Skin_dep...

[amluto]

The tin is painted, and paint is nonconductive. A very thin long slit in an otherwise conductive surface or mesh can be extremely leaky.

[yosito]

Reminds me of a joke my dad used to tell:

Dad: What's five plus five?

yosito: Ten!

D: How many fingers do you have?

y: Ten!

D: What's an aluminum can made out of?

y: Tin!

D: Wrong! Aluminum!