I want to make a rare mob museum in my survival world but I'm having difficulty separating the armoured mobs with the unarmoured ones. One way I thought of was sunlight but helmets break after a while in sunlight but I think it's doable. Another way could be a way to separate them all into separate cubicles where I can see which mobs are special and kill those less cool. If anyone has any ideas I'd love to here them.
At my base I have an underground pen system with surface access which consists of a recessed bay with a piston controlled floor which drops into a water stream that deposits them into the pen. I used this to load up the pens with a few animals for breeding but i've also been recently using it to trap zombie villagers for curing in one of the empty pens - when i see one on the surface, i usually kill any other mobs in the vicinity and lure the zombie villager into the bay - the button is at the far end so as he approaches me i press it and the pistons open and in he drops. You could so the same thing to trap your selected mobs, as i guess you are targetting either zombies or skeletons. You'll need some name tags handy to name them to prevent them despawning, unless they've picked up a dropped object (zombies that is). This method traps only the ones you want.
I use this technique mainly at night, the only issue is if you see a mob you want to collect but its near dawn - he may burn up before you can reach your pen, but some throwable potions of fire resistance can be used to protect him.
Some screenshots of my pen setup:
External view of one of the pen loading bays - the wooden button can be seen at the back which opens the floor
At the button end with the floor open, leading to the water channeling part