Hi John
This does not look at all like olive wood.
But!!
When you touch the pen does it have a silky feel? Did you notice the aroma whilst turning? - sort of sweet?
If so, then there are number of scenarios:
- The wood is extremely young and whilst drying developed an fungicidal growth or young wood that has been in a damp place for a long time?
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- A reaction to your finishing process ie CA etc - will dissolve the fungi
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- I am not suggesting it, but I have come across pressure filling the wood with dye to enhance grain unaturally - this only possible in young wood or again damp and spongy wood - the finishing will alo possibly dissolve the dye.
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Try this - diassemble, rub back to wood then rub with neat alcohol, and re-polish with a friction polish, wax based.
Please let me know how you get on - I am intrigued - you can if you want send me the pen for a thorough analysis - I will return it unharmed! Email me at mik@mikpens.com