Double Time Flattening Stone, Pink alumina

This is an in depth review of the the pink oxide flattening stone from sharpeningsupplies.

The good folks at sharpeningsupplies are always working hard to provide the best in sharpening, with the introduction of the DTFS pink oxide stone we get to see their innovation and sincere dedication to the craft. But what exactly is Pink alumina and what makes it so special? Pink aluminum oxide is created by adding chromium and other elements to aluminum oxide, that are then electrically fused together at high temperatures. It is the addition of chromium that gives this abrasive its signature pink and ruby colors, this also gives it exceptional strength and wear resistance., though it remains just as hard as white aluminum oxide.

UPDATE 11/24/23: This stone was released on a limited run and though it may have been available at the time of writing this, it may no longer be available for purchase. Though we hope sharpening supplies brings it back in the near future. Please continue reading if you truly love stones or to feed your curious mind as it is a good and insightful article.

First Impressions

When I removed the stone from the packaging and held it in my hand, the first thing I noticed was that it was heavy, heavy for a lapping stone. Infact it felt heavier than their original DTFS. It measured 10"Lx4"W and was exactly 1" thick through the entirety of the stone. The 120 grit side was rough but not course, the 280 grit side was an amalgam of rough and smooth grains. When held to the light you could visibley see the glittering abrasive particles densely running across the surface of both faces. The channels running through the stone seemed shallower than on the original DTFS but did not seem to be too big of an issue. Being impatient I sunk the pink DTFS in water and to my suprise it wasnt long before it was ready to use. I ran the first stone I could grab (a naniwa traditional 8000) over the face of the lapping stone and in less than a minute bubbles and slurry started filling and pulsating through the channels of the stone. Swarf and mud were being pulled from the stone, the stone was starting to gradually get bright white. I already knew this was going to be a great lapping tool.

Testing The DTFS Pink Alumina

After marveling at the stone for a bit I got to testing it right away. I performed a number of tests on the stone looking for some key features, those were: flatness, hardness, wear rate, water absortion, drainage , cutting power and its overall performance. The following is list of those tests and their results.

Flatness:

Right of the box the stone is virtually flat, I started with the most common test and that was done by using a straight edge, placing the straight edge along the stones length and along its width showed the stone to be flat. I performed addtional tests to check for flatness this included visual inspection both with and without the assistance of a maganifying eye device, this also showed the stone to be flat. Next I perfomred a pen light test checking for any signs of light, this would show if there were uneven parts of the surface. This also showed the stone was flat. Lastly I placed the stone on a glass lapping plate and found the the stone to be flat.

Hardness:

In order to test the stones hardness I used my Mohs testing kit, this utilizes a series of pointed and numbered instruments of varying degress of hardness. You take one of the intruments and scratch the surface of the object your testing until you are able to effectively scratch it. The Mohs scale runs from 1 to 10, with 1 being a mineral like talc and 10 being the hardest which is diamond. I was able to make my way up to 9 when the stone was dry. I also tested the stone after it had been soaking in water, when left in water for 1 minute and 30 seconds it remained at 9 however when left to soak in water for several days the number 8 instrument was able to lightly scratch its surface. This was quite a difference from the original DTFS made of green silicon carbide which I was able to scratch with the number 8 instrument dry and 7 when wet and was able to make a deep scratch with the number 9.

(Pictured is the scratch left by the number 9 instrument in my Mohs kit when the stone was dry)

Wear Rate:

In order to test the stones wear rate I used 10 different sharpening stones with varying degrees of hardness, they spanned from soft to medium to hard. After flattening the stones I used a digital caliper to measure the thickness of the lapping stone, checking each inch of the stones length to the best of my abilities. My measurments showed the pink stone had gone from 1" thick to just a hair under at 0.99" this was another major plus from the Original, when I performed the same test on the original green silicon carbide DTFS It had gone from its original thickness at 1" to a significant decrease at 0.92" after a year of heavy use the original had gone down to 0.87". UPDATE: I included a new test using a 400 grit diamond plate for about 1 minute to measure the pink DTFS wear rate and this brought it down 0.97" this was nothing more than expected since diamond abrasives are very agressive. Time will be the ultimate factor here since this stone is very durable. One final test we did as mentioned above was leaving it fully submerged in water for 2 days, though we were able to scratch the surface with a less hard instrument this was not a siginificant amount of wear as it was only the top most part of the surface. The instrument did not embed deeply into the stone. It also did not fall apart, flake, chip or break down after being left in water for such a long time.

Water Absortion:

Upon prepping the stone for use I noticed it had a fast water absortion rate, meaning when fully submerged in water the air trapped in the stone escaped quite quickly and the stone had soaked up plenty of water. After the stone had fully dried the following day I tested its absortion rate again this time it was timed and I found that between 58 seconds to one minute and 15 seconds the stone was ready to use. If you do not allow a lapping stone to absorb enough water the combination of the lack of fluids and build up of waste will cause your sharpening stone to adhere to the lapping stone, it can also slow the stones cutting power since there isnt enough liquid to carry the abrasive particles around. This was also quite different from the original DTFS that when fully submerged in water after a dry spell roared and bubbled agressively, taking about 90 seconds to be ready for use.

Cutting Power:

I simultaneously tested the stones cutting power with Its wear rate, since both would require using the stone for its intended purpose. Unlike the sharp jagged grains of silicon carbide, pink alumina grains are sharp and angular. I expected this stone to have less cutting power than the original DTFS. The stone has pretty agressive cutting power, It made quick work of soft stones like my king stones and my suehiro stones, a badly dished out 800 grit king stone took just one minute and two seconds to be completley smoothed out. It had moderate cutting power on medium grit stones, It took about 2 minutes and 37 seconds to correct a medium density stone made by Yoshihiro but slowed slightly and took more time when it came to harder magnesia bonded and ceramic stones. It took about 4 minutes and 52 seconds to correct a worn down shapton 120 stone. It took about 5 minutes and 22 seconds to remove a gouge in a naniwa pro 600 grit stone. When compared to the original DTFS it cut slower and was not as agressive.

Pros and Cons

This stone does not have more than one con but I still feel its important to list pros and cons no matter how few they are. A product cannot reach its full potential without honesty.

Pros:

• Large size and generous surface area, this stone like the original is 10"Lx4"w giving you plenty of space to ensure not a single spot on your stones will be left untouched.

• Dual Grit, this stone is a combo with 120 grit on one side and 280 grit on the other. There is currently no other known dual grit pinlk alumina lapping stone on the market.

• Thickness, this stone also like the original is 1" thick this paired with the material its made from means one thing, IT WILL LAST.

• Higher strength and wear resistance when compared to all other silicon carbide based lapping stones

• Price point, for a quality stone of this size below $70 is a very good deal.

Cons:

• The grooves on the DTFS pink alumina are shallower than on the original double time flattening stone. This did cause the stone to get clogged faster when working with stones that were splash and go and other stones that produced thick mudd like the Naniwa super 220. This slowed the stones performance only slightly.

• Because of its lighter pink color it does get dirty in busy shops like ours, though this "washes" away when you start to use it but it will get dirty again. A vicious cycle thats a lot of fun in between. Not a major con by any means but something worth noting. merely a natural comestic blemish.

The Final Take

I have been sharpening for some time now and my love is for stones. I have always preferd them since my great grandfather started teaching me on his Norton bench stones. I have used and collected too many stones to count, so when new ones come out I am always eager to try them and add them to my collection. The DTFS pink oxide version is one im particulary joyed too have gotten. I would rate this stone 10 out of 10, It is a well made stone with a large size that will be hard to find a home for, though it has taken permanent residence on my bench. It has moderate cutting power and is agressive enough while still being gentle enough to resurface some of my Japanese natural stones, my indonesian naturals and some of my american naturals like my Hindostan and Lilly white. It does take a bit longer to resurface harder stones but it will not break down as easy as silicon carbide in doing so. Its definitely a game changer in my opinion since there is currently no other dual grit pink oxide stone on the market. Again you have the 120/280 combo. If your a sharpener, a woodworker, a chef or anyone whos looking for a lapping stone to last the length of time, this it.

We hope you found this article helpful, let us know by leaving a like and as always the comments are open, stay sharp folks!