Let me explain why I'm asking for this:)
I have some nice OG cherry caps (standard white/beige) which are like 30 years old and a bit yellowish (I did bath them in oxygen peroxide to white them up a bit), they have such a nice retro look now.
I have added some R5 bottom row newer caps to it and those are a bit brighter - I want to get them yellowed quickly, so they match rest of the set
Would putting them on window sill be enough? So I wouldn't have to wait like 10 years to go yellow?