rust, tarnish
錆 centers on the deterioration of metal surfaces: rust forming on iron or steel, and by extension tarnishing or losing luster. Both meanings describe a metal-specific form of decay.
錆 combines 金 (metal) with 青, which likely contributes the sound and may have originally suggested a blue-green patina or tarnish on metal. The exact historical development is uncertain.
Metal 金 that turns the color of blue-green 青 is rusting. Picture a copper roof developing a green patina: that is 錆, rust and tarnish.
For ショウ, imagine a rusty old car that you need to show to a mechanic: show -> ショウ, and the rust is the reason you're showing it.
rust
to rust; to become rusty
stainless steel
rusting; onset of rust
red rust
to rust; to become rusty
paying for one's mistakes; getting one's just deserts; suffering the consequences (of one's own actions); reaping what you sow; making a rod for one's own back
rust
iron rust; iron hydroxide
to become rusted together; to become rusted shut
rusted; rusty
sword with rusted edge; useless sword
rust-proofing; anti-corrosive
rust (colour)
anti-rust; rustproof; anticorrosive
anti-corrosive (agent); anti-rust; corrosion inhibitor