I recently had a conversation with a potential customer about red coral, and, well, it inspired me this blog post!
You probably know that red and pink coral can show as many colors as many existing species. Different colorations may also indicate different processing techniques, though.
By the way, I'm talking about jewelry making corals, as bamboo coral - the shining, smooth one above -, or madrepora - the reddish, stony one below. You can't go wrong here, because the mediterranean (or japanese) coral costs ten times more.
The question was just about coloration, and the answer is that, differently from gemstones, coral is not actually dyed, but lacquered. Sometimes, the result of this red or pink lacquering may look "unnatural", but that doesn't mean it is not actual coral the one you're looking at. It is the species that counts.
So, I'd like to add a tip good for everyone, don't be scared to buy something just because is too red or too pink, and rather buy what you like! It is highly improbable you're purchasing plastic, or a painted rock!
...and that was my opinion until I found out that a lot of low-quality corals are sold with commercial smart names: apple coral, tiger coral, white coral, fossilized coral, and so on. Those ones are actually bleached or dyed sponge coral!
I use just bamboo and madrepora coral. Bambo coral is a precious coral, together with red and pink corals (Coralliums), gold coral (Primnoa), and black coral (Anthiparian). Differently from these latter, bamboo it is often filled and red lacquered.
About madrepora I couldn't find any clarifying information: someone defines it precious and someone else semiprecious, someone as a corallium and someone else as an acropora. I don't know what to think, but if it's part of a coral reef, as someone says, then it is not from deep waters, where precious corals live. You do the math...
Anyhow, I think a buyer would rather want to know if the shining color of bamboo coral fades away with the passing of time. It does not. And here it comes my second and last tip: colored or less, coral should be cleaned from time to time with a cloth soaked in natural liquid wax.