It's a natural coral from Indonesia, called Madrepora from their handycrafter, it's handworked piece by piece. The color is completely natural, with shades from orange to red.
The manufacturing process starts diving for many pieces near the indonesian beach that are (still) rich of this kind of coral, then they are cleaned, polished and finally they are lived to dry on the sun. You can see some of these pieces obtained in the upper picture. After that the coral is dealt and worked to give shape and size needed to realize jewels in sterling silver.
