The Nest of the Lotus Flower (II)

This is a follow up to the previous post, specifically in regards to a question Ward Wilcox asked:

I have heard there are a two or more lines of Sigma Stones. The line sold by Lee Valley are different than the ones Chris purchased. Do you need to soak the Sigmas? The Sigma display on Lee Valley claims they are soft but cut very fast. DJY states the 1000 grit is too slow if I understand him correctly. How do Sigmas measure up to Shapton pros?

I asked Stuart Tierney of Tools from Japan to provide an answer, as he has a much better picture of the scene than I do, and here's what he wrote - detailed and long enough to merit a second post in this thread:

Hi Ward, Stu here.

There are indeed two 'full' lines of Sigma Power stones, plus a 'back catalog' of various others that nobody you know of (except me) has heard of.

The one LV have are 'Select II' from the updated original series. Let me explain...

Originally there were 2 'Select II' stones, the #1000 (grey) and the #10000 (yellow). About 2 years ago, give or take, Sigma Power expanded the 'Select II' line with a #240 (bright green), a #3000 (darker green) and a #6000 (orange/yellow).

These are singularly unique stones. All use Silicon Carbide as their abrasive and have NO binder. Every other manufactured stone has a binder of some kind to hold them together, these ones don't.

This is a double edged sword...

It's good because Silicon Carbide is very hard and will cut virtually any blade steel with ease, and because there's no binder the entire stone is 'good stuff'. So they'll cut anything and do it very quickly.

It's bad because a binder tends to allow the maker to adjust the 'friability' of the stone, in essence, how quickly the stone breaks down with use. With these 'no binder' stones, that 'adjustment' is lost to a large extent. It's very apparent in the 3 coarser stones (240, 1000, 3000), less so in the finer 2 (6000, 10000) because the finer stone's particles are smaller and in better contact with each other, they tend to 'hold together' a little better.

The funny thing is, this 'friability' is only a concern when the steel is relatively soft and easily abraded. These stones were specifically developed for High Speed Steel which is usually quite hard and very tough, both making it quite difficult to abrade with conventional sharpening stones. If you use hard HSS on these stones, they change significantly into stones that are actually quite 'flat', still fast and very effective. On 'normal' steel, they do tend to dish a little faster than I'm happy with, but they do work faster than almost any other stone so the dishing is less (because they work faster) than it might otherwise be. 

There are 3 additional stones with the 'Select II' label now, a #400, the #1200 Chris has here and the #13000 which is also shown here.

The #13000 has been around for many years, but Sigma Power have changed the label on it from 'ceramic' to 'Select II' as internationally, the Select II branding is more widely known and recognised. The stone is the same, the label has changed, nothing more.

The #400 originated late last year from a request for a stone that was coarse, but showed stronger dish resistance than the #240. 2 stones were produced, a silicon carbide stone similar to the existing #240 and a white alundum (WA) stone, with a binder in it. The SiC stone was an improvement over the #240, but still dished too quickly. The WA was not as fast as the SiC stone, but the dish resistance was excellent. As that was the desired property, the WA stone went into production. As it deals well with HSS, it was no concern to use the brand recognition of Select II on this stone, so that's what it got. A pink label no less...

(It was cheaper too. I still have both prototype stones and would like to see the SiC stone go into production as well. The knife sharpener folk will love it!)

The #1200 came into being from concerns about the Select II #1000 dishing too rapidly for many tool sharpeners when used with Western style tools. I asked for the same stone with some binder in it to 'firm it up' a little. The straw that broke the camels back was the FWW review where the ceramic #1000 did quite well, but the Select II #1000 did poorly.

The #1200 was the answer to that.

The Select II #1200 is again, a WA stone. The abrasive is finer (genuine #1200 grit), the ratio of binder to abrasive is changed toward more abrasive and the binder is a tougher, less likely to break down type.

As a result, the #1200 is very hard, has very strong dish resistance but still works quite quickly. Because of the high ratio of abrasive to binder, this stone still works well with HSS and also deals with 'normal' steel well.

Now here's where the line is blurred somewhat...

The #1200 has a Select II label on it, but it's closest relative is the older Sigma Power 'ceramic' line of stones, specifically the #1000 'hard' and not the Select II #1000.

The 'ceramic' line of Sigma Power stones have had sporadic availability outside of Japan for quite a few years. When I first started my little store, I made sure I was able to get these stones and make them available on a more consistent basis.

Not long after starting up the store, I contacted Sigma Power directly (previously through a dealer) and they decided to deal with me directly, which means I 'have their ear' when it comes to new products.

Their 'ceramic' line are more conventional stones with a binder in them, in this case it's a true 'ceramic' type binder and the name reflects this. In many other 'ceramic' type stones, the ceramic signifies the abrasive is a manufactured abrasive so is consistent and tougher than naturally occurring types. In the case of other 'ceramic' stones, the binder may be a ceramic material (fired at high temperature and fused together), a resin, a plastic or a baked binder. These binders allow the maker to fine tune the working characteristics of the 'stone' (is a plastic/WA concoction really a 'stone'?) to get what they want from it.

Anyway, the Sigma Power ceramic stones all have a binder in them and are available in #120, #1000 (hard and soft), #2000, #6000, #8000 and #10000 as well as the #13000. The #120 has SiC abrasive in it, the rest use WA (except the #2000 which has pink alundum. Long story but it's slightly different) and are fired in a kiln similar to a coffee cup.

They come from the same company, the labels are different but the ceramic were the 'original' stones, the Select II are newer and borrow from the 'ceramic' line when appropriate.

And the #6000 above?

It's from an even older line of stones, before there were 'lines' of stones. It got the 'ceramic' name when Sigma Power stuck a base on it.

So it's technically a 'ceramic' stone, just as the Select II #13000 is technically a 'ceramic' stone and the #1200 is in Sigma Power speak more a 'ceramic' than a 'Select II'.

I hope that's not too confusing, but with these two lines of stones borrowing from one another it never going to be an easy task to completely separate them.

Stu.