Hard to say from the photos, could be a Translucent. A good soaking in Simple Green & water, 50/50 will get it clean, but could take months depending on how much oil has soaked in and how clean you want it.
When I get an Ark I clean with Oven Cleaner and dish soap then if it is flattish and smooth, I try a razor on it. If it was well used it may have a nice burnished finish on it that would be a shame to remove by lapping.
Lapping is done with about $15 of lose Silicone Oxide, you will ruin your diamond plate trying to lap an Ark.
Here is a good thread on cleaning and lapping Arks.
They can be very nice finishers after an 8 or 12k edge. An Ark edge is crisp and smooth, it is a unique edge.