Natasha wrote:Umimatsu is not fragile, it is very comfortable raw material, black coral contains a lot of protein, so it is resilient, it is well-cut with any tool in all directions, perfectly polished.
Umimatsu is the Japanese word for black corals but there are numerous types of black corals... some of which aren't even black. While I'm always loath to challenge your "alternative facts" given the fiery response it will no doubt illicit, this is still an educational forum and we are principally concerned with the sort of facts that are related to observable reality. (Well at least I hope we are.. sometimes I wonder. )
So FYI but mainly for the benefit of anybody confused by your earlier comments, there are black coloured corals, pink corals, red and brown hard corals and lots of much rarer corals like the famous golden hard coral and even green coral. In the Japanese netsuke tradition and our netsuke literature many of those different types of coral have been lumped together and routinely referred to as umimatsu although some corals like the pink corals do have other more specific Japanese names. All the corals and indeed different parts of individual coral species have their own workability characteristics and many diverse qualities although according to Bushell (13/ 2:6), "As material, umimatsu is more acceptable to collectors than carvers. Leading carvers naturally avoided the material. It was prone to crack, crumble or chip. Carvers find that it is risky for carving details and subtle effects."
That said.. some species of black corals are as hard and uniform as you describe.. and they will indeed take fine detail. Many others however are far less so.. some are extremely brittle and structurally much more varied, but with many wonderful colour characteristics, textural qualities and translucency which still makes them highly desirable as a netsuke carving material. The species of coral that are most commonly seen in the Japanese Netsuke tradition are those that occur around the coast of Japan and Western North Pacific.
Here is a netsuke carved from a particular black coral species.. while structurally dense you can see thick layers partially separating.
Here is some raw dense black coral from my personal collection..
And here is a dense black Umimatsu carving done by the very talented Dutch carver Ko Baas from some coral I sent him as a gift.
But as I said before... there are other types of Umimatsu, such as that used in this famous Kanman netsuke.. this would also be a black coral but its structure is a great deal less dense than the previous examples. The material also has prominent colour inclusions and some areas that are very much weaker that surrounding dense dark areas.
Simply put.. black corals are often simply not uniform in structure irrespective of their overall molecular composition and can be strongly veined with softer brown or red material..
Then there are the much rarer umimatsu types like the commonly referred to "golden corals"..
Here's a pic of what some of that might look like in the raw form.. again from my personal collection.
and the same material partially worked showing some of its colour potential..
As you can perhaps see from the cross section the structure of that coral is even less uniform and dense than the blacker corals and it is as Martyn correctly said.. extremely fragile,thinly layered and is indeed very difficult to work successfully. What's more, the fine dust produced if carved with powertools is also very dangerous and more than a few carvers have over the years been badly affected by it despite using powerful extraction fans, including one very seriously. This close up image posted by Alain Ducros gives some insight into it's potential weaknesses.. a layer might suddenly and without warning crack or crumble.. its extremely unpredictable and virtually impossible to impose a design onto. It has to be approached with the greatest respect and sensitivity.. through an intimate dialogue between the carver and the material. IMO, carving this sort of umimatsu is really one of the most intellectually challenging of materials to work in..
but its incredible richness and beauty makes it decidedly worthwhile if one can pull it off.