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I have a ceramic mortar & pestle, approximately 10 cm across, that I use primarily for grinding whole spices. When I bought it about 15 years ago, only the exterior of the mortar (and a small amount of the interior) was glazed; the interior had an unfinished, rough texture akin to bisqueware. Similarly, the bottom 2–3 cm of the pestle was also rougher in texture.

After many years of usage, this rougher texture has been smoothed out in the center of the mortar and at the end of the pestle. I think (though it may just be confirmation bias) that this makes it less effective at grinding, as the spices are not "gripped" as much by the ceramic surfaces.

Is there a good way to re-roughen the grinding surfaces of this mortar & pestle? Or would it not be worth the trouble to do so?

Michael Seifert
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1 Answers1

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Potter and maker of ceramic mortars here.

Should You: whether or not a mortar actually becomes smooth enough to affect grinding inside depends a lot on what kind of ceramic material the mortar is made from, and what temperature it was fired to. I have a steel-furnace-fired kaolin-based pharmacy mortar that's over 100 years old that I still use, and it's just rough enough (sandstone-like) for good grinding. On the other hand, many inexpensive handmade ceramic mortars are made from low-fire earthenware, and will totally grind smooth with use. Once the interior reaches the smoothness of 'polished wood', it's going to be harder to grind seeds (but see below). Mashing of leaves, roots, and aromatics should be unaffected.

How To: sandpaper. Get some 20 to 50 grit (depending on how rough you want it to be) wet/dry sandpaper. Dampen the mortar (you do not want to breathe the dust) and sand away. The carborundum of the sandpaper is harder than any but the hardest ceramics, and it should roughen it nicely. Then scrub out the mortar and let dry. If you have trouble sourcing low-grit wet/dry sandpaper, use a very rough grinding stone with a Dremel-like tool instead.

Think About: if what you do is primarily grind spices that come in the form of seeds, think about getting a Japanese-style "combed" texture mortar (see pic). These mortars are specifically designed for grinding seeds, and the rough interior won't grind smooth, particularly if you use the recommended hardwood pestle.

japanese-style combed texture mortar

FuzzyChef
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    Dang. Now I have a new kitchen gadget for my wish list. – Stephie Dec 02 '21 at 18:58
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    "you do not want to breathe the dust" - I wonder about the advisability of ingesting the "ground-smooth" dust over the years (genuine ignorance here, not an allusion). If this may be problematic, maybe replacement is advisable in any case (with something more wear resistant)? But my instinc says it may not be significant... – frIT Dec 03 '21 at 09:29
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    I have a boron carbide mortar that would argue with your claim regarding carborundum, but I guess that would be covered by the "but the hardest ceramics" part. +1 Anyway. Funfact, you can generally roughen a surface with a softer material it just takes more time. Carborundum sandpaper should do fine. – Stian Dec 03 '21 at 09:38
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    @frIT ingestion of (most) mineral dusts is far less of an issue than inhalation - we have far better mechanisms for removing bits of unwanted but not actually toxic stuff from our guts than from our lungs – Chris H Dec 03 '21 at 15:04
  • The very hardest seeds (fenugreek) won't care how rough it is, because you have to hit them pretty hard to break them up, but roughness certainly helps with things like coriander where pressure and a grinding action is key. Mine is also pretty smooth. I wonder if I have any really coarse wet/dry at home to give it a try (I know I have much finer) – Chris H Dec 03 '21 at 15:06
  • Thanks, this is extremely useful! One question, though: did you really mean 20 to 50 grit waterproof sandpaper? And if so, where would you buy it? My local big-box hardware store only stocks down to 60 grit, and the coarsest paper that's marked as waterproof is 600 grit. – Michael Seifert Dec 03 '21 at 15:22
  • @MichaelSeifert I can attest to the fact that waterproof 40 grit sandpaper exists. Can't tell a thing about supplies in your area, of course. – Mołot Dec 03 '21 at 15:46
  • @MichaelSeifert I suggest going to a lumber store or a different, better stocked hardware store. Or order online. 60 grit would also be OK if that's what you can find. – FuzzyChef Dec 04 '21 at 01:05
  • @frIT: also, if you're ingesting a migrogram of dust per use, it really doesn't matter. Mind you, if you have shoddy mortar that's giving off a visible amount of grit every time you use it, you need to stop using it. That's really bad for your teeth. – FuzzyChef Dec 04 '21 at 01:09
  • @StianYttervik what does one do with a boron carbide mortar? – FuzzyChef Dec 04 '21 at 01:09
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    @Fuzzychef It was originally meant to grind and mix ceramics before shaping and sintering but the project got canceled and the lab shut down for renovation. Since it was still newly purchased, still in its wrapping I decided to adopt it for culinary purposes. It does fine for that but the metallic sound it makes when you pound seeds is unnerving. It is like striking an ambolt with a hammer, only an octave or two higher in pitch. – Stian Dec 04 '21 at 08:38
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    @StianYttervik seems like you could sell it to a ceramic artist and get a better one for food. Among other things, boron is not good for you. – FuzzyChef Dec 05 '21 at 05:36
  • @MichaelSeifert The coarsest I've got here (i.e. the coarsest I can easily buy) is 240 grit. I've got coarser in work. I do have some 80 grit paint removal sandpaper that works wet for a little while, but it doesn't do anything to the ceramic. Also for a small mortar you need something quite flexible. The narrow strips of emery cloth might do the job – Chris H Dec 07 '21 at 10:59
  • I had no idea that sandpaper was so hard to source. Adding another suggestion to the original answer. – FuzzyChef Dec 08 '21 at 19:10