Thread: Scratches after lapping a Shapton 16k glass stone

Hi all,

Until recently I was using the Shapton high carbon glass stones up the the 8k (max for the HC) and CrOx for shaving, and was generally happy with the results. Always wanting more, I went and purchased a 16k glass from the 'bay that came pre-lapped. I used it on two razors, and the results were exceptional. 8 passes on each side of the razor before CrOx gave me the best shave I've had.

However, since attempting to lap the stone I've had nothing but trouble. Initially I used 600grit Norton sandpaper on a granite slab. The stone was still pretty flat, but I used light pressure until all the pencil marks were gone. I tried finishing another razor and it *felt* very rough, I could tell something was wrong and stopped to wash the stone again, thinking I had particles from the sandpaper in the stone. Same result.

Since this I've tried: using my lower grit stones to make it smoother, using a hard tomonagura (this only raised a tomonagura colored slurry), and finally I caved and borrowed a friends' Shapton glass lapping plate. Thinking I had this nightmare behind me, I gave a few passes on a razor straight from my 8k that had an impeccable mirror finish... The resulting scratches looked like I was using my 2k!

So, my question is, do I need a stone that is equal in hardness to the 16k and higher in grit to give it a smoother surface? After a bit of reading, it sounds like the HC glass stones may be softer and not equal to the task.

I did ask the seller how he lapped it initially, he said with a plain old DMT D8C. Could the Shapton glass lapping plate I used not have been as broken in as the DMT, therefore leaving bigger scratches?

Sorry for the long post, but I'm pulling my hair out here.

I use my DMT 325 for a few swirls every time I use my 16k Shapton, with no ill effects at all.

+ 1 to what Blix said.
I use my DMT 325 to lap everything, even some old vintage oil stone to remove sractches and even them out. I've used my DMT some many times it has changed color, but will still cut the h*ll out of a grass jar.

Maybe lapping with the 600 grit paper and granite slab embedded sand in that Shapton and you did not lap down enough with the Shapton Lapping plate to remove the sand. I think that if you get a DMT 325 and lap that 16000 down enough, it will remove any possible flaws.

I look at my Shapton 16000,think of how much it cost me and I won't touch it with anything but my DMT 325.

Thanks guys.

I was worried that the sandpaper had some ill effect. I did have a DMT at the time but it unfortunately turned out to be not remotely flat. Laying it on a piece of marble, I could see a gap where the bend was!

I'm still waiting for a replacement, so I guess I'll have to make do until then.

I've used the DMT 325 all the way up to 30K, but don't use it below 1K. I've had no issues.

Well, I got my hands on some 3M 5 micron lapping film and used it on the stone, it seems to have fixed the problem completely.

I guess the Shapton Glass lapping plate I borrowed wasn't completely broken in, and was leaving peaks in the stone...?

I bought a 16k stone a month ago and have been pulling my hair out. 8k leaves a mirror-like shine and 16k leaves deep streaks like a 1500 grit stone would leave.

Then it dawned on me - I'll bet the Shapton 16k and 30k have periodic manufacturing issues simply because a supplier mistakes those 4 zeros for 3. So, in every few batches you might be getting a bunch of grit added to a batch of 16k stones that's 1600.

Knives & Stones in Australia kindly offered to refund the stone & shipping and will arrange to get this particular stone back to Shapton to find out.

I don't think you're losing your mind at all.

First of all, Shapton does not make a 1600.

Second, "every few batches?" Do you really think any company could function that way?

Did you lap the 16k? If so, with what?

What other GlassStones do you have?

interesting... I just acquired the 16k GS. I too noticed the scratches on it after lapping (DMT 325) but only under
a 40x loupe. I lapped it again but very softly for quite a while....20 mins or so and the scratches were still visible. I decided to just go ahead and use it anyway on a pretty average stainless blade I got on ebay. First I gave it the norton 4/8k treatment and then straight to 16k GS.... followed by a few back strokes on crox balsa then strop. 50 linen 50 leather. The result was the finest straight razor shave I've had yet. I'm well pleased with the 16k finish. It might be too early to say but it seems to me to be a sharper and smoother finish than the nani 12k. not selling the nani yet though. lots more experimenting to do.