Rainbow toning

Pity it is a bit irregular.
I reason that it would be stupid (due to the value), to rainbow tone it on one side only, using a carefully temperature controlled hot plate, and carefully timed exposure, but it could be possible.
Whatever the case, be it temperature of chemistry,
it
has obviously been exposed on one side only,
perhaps in a drawer made of wood, that has an active natural resin in the wood.
For me, the toning adds to eye appeal but not extra value,
because delicate rainbow toning is unstable, and an item such as this needs to be in an air tight enclosure to keep the toning as you see it now.
Question:
Would the slab be sufficiently air tight in the long term ?