Ethnographic Arms & Armour - View Single Post - A huge iron mortar & pestle for ID and comments

Helleri · 29th October 2018, 11:58 PM

Sorry for the late reply...

So firstly, the whole magnet to test for cast iron thing is a myth. Magnets will readily attract to cast iron as they would any room temperature ferrous metal. All a magnet tells you is whether or not the item has a ferrous metal content.

Secondly, not all that is cast is cast iron. A true cast iron has a ridiculously high carbon content. There are reasons for this. Firstly they get hotter a lot easier. Whenever you have a more conductive material touching a less conductive material there is resistance (this is all pertinent but it's going to take a while to get there, bare with me). The whole wants to equalize. The resistance between one material and another builds molecular excitement that heats the more resistant material even more.

This is why some steel pots/pans are copper clad. the copper is very conductive. the steel not so much. So a little heat into the copper translates into resistance that builds a lot more heat in the steel. This works with cast iron because there is a high (higher than high carbon steel) carbon content. the carbon is less conductive than the iron. So it takes less heat to get a cast iron pan very hot, very quickly (they are fuel conservative).

A high carbon content also makes them very hard. This means they have a low friction surface (so they require less lubricant) and they resist permanent surface deformation (scratching).

These are the reasons why something like a cast iron pan is made of this iron with a ridiculously high percentage of carbon in it by weight. Because it's made for heat applications (cooking low fusible point metal casting etc).

However, cast iron is also very brittle. Hardness and toughness are not the same thing. They are mutually exclusive to some degree. You can make something harder (resistance to permanent surface deformation; Like scratches and dents). Or you can make it tougher (resistance to self separation; like chips and cracks). But generally when you make something harder you make it less tough. When you make it tougher you make it less hard.

So with this foreknowledge about how all that works in place we can now think about this logically. Would it make sense to make a pestle and mortar out of a material that is brittle and better suited for high heat applications? The obvious answer is "No". You'd want it to be made out of something softer. High/medium/low carbon steel as well as wrought/ductile iron are all better options. Now there are different grades of cast iron. So it's possible that it's just on the edge. A little higher than the highest carbon content crucible steel . But a little lower then what would be used for cooking.

So we can reason that this is obviously on iron product. But likely not the same grade of iron as the cast iron used on say a Wagner skillet. That's what can be discerned about the composition without handling the piece in person and doing some tests.

What test would I do to narrow it down? About the only reliable one. A spark test. This is fairly non-destructive (although it would leave marks). And it works basically by touching some part (obviously a part that isn't going to be visible on display) with a grinder. The spark shower, shape, spread, arc, and color can inform one as to what the composition is with high precision.

In case you are interested in knowing how to do this test yourself for narrowing down that composition (it's not hard) here is a link to a PDF on the subject: Metal Identification

Now onto application. Again we can reason this out. This is extreme overkill for pounding out some flour or meal in my estimation. You've a much harder and heavier set of materials than is any where near necessary to efficiently grind grain.

This seems more on the order of what is used to crush pigment minerals for paints and dyes. Or Borax and alum crystals for flux and fixants. Or Limestone to be baked into quicklime. Or large salts for glazing. This seems like it would fit better around a dry salter's (someone who makes inks and dyes) or a potter's setup. Even a small foundry more so than a kitchen.

Regarding construction I would say that the mortar definitely looks cast. the dot and line on it is a classic Sprue and seam mark. We even see scoured marks going against that grain. Indicating that there was left over scales/scabs which needed to be chiseled off. On either the mortar or the ball you can see the striations in the grain pattern that even indicate direction of molten flow.

The ball seems to have a large sprue mark (perhaps two?).
But on the ball there is that interesting smaller bit that looks squarish. That could very well be a pin that in part secures the ball to the shaft. So the peen at the end would keep the ball from falling off the shaft and the pin would keep it from moving up the shaft or turning on the shaft (if it is indeed a pin).

The shaft is definitely not cast. But manually hammering out a nice round round like that is fairly difficult and time consuming. Likely it was extruded and then drop forged. Which is basically where the smith has a die that the piece is suspended over. And the piece would be moved and rotated against the die as a large hammer is lifted and dropped (not driven with force but let to fall under it's own weight) onto the piece causing it to conform to the shape of the die. I wouldn't doubt it even if the rims of the mortar got a few turns against a drop forging die post-cast.

I've not seen a pestle and mortar quite like this before. I've seen ones this large and even larger. But those are invariably made of wood. I don't think this was a mass produced thing. This has the appearance of having been made in a workshop for a specific purpose.

I couldn't even begin to speculate on a date. The processes that would have gone into making this have been around in Europe at least since the middle ages. There isn't anything definitive in evident process that would nail it down precisely as to place or time of origin.

I hope what I have laid out here was not too much of a bore to read through and that it is at least somewhat helpful.

[Edit: the seam is not an indication that the mortar was made in two halves. Just that it was a two part mold for a single piece and the seam with it's sprue is simply where the mold would have been opened.closed at. Check the bottom of the mortar for another sprue mark (this will give an indication of mold orientation)].

[Edit 2: The 8 mark is likely a missed/skipped blow from a setter. That is what looks to be the exit hole of what I believe to be the pin I referred to earlier and it would have been peened there. If there were a makers mark it would likely be on the bottom of the mortar].

29th October 2018, 11:58 PM	#6
Helleri Member Join Date: Jan 2016 Location: Boulder Creek, CA. Posts: 202	Sorry for the late reply... So firstly, the whole magnet to test for cast iron thing is a myth. Magnets will readily attract to cast iron as they would any room temperature ferrous metal. All a magnet tells you is whether or not the item has a ferrous metal content. Secondly, not all that is cast is cast iron. A true cast iron has a ridiculously high carbon content. There are reasons for this. Firstly they get hotter a lot easier. Whenever you have a more conductive material touching a less conductive material there is resistance (this is all pertinent but it's going to take a while to get there, bare with me). The whole wants to equalize. The resistance between one material and another builds molecular excitement that heats the more resistant material even more. This is why some steel pots/pans are copper clad. the copper is very conductive. the steel not so much. So a little heat into the copper translates into resistance that builds a lot more heat in the steel. This works with cast iron because there is a high (higher than high carbon steel) carbon content. the carbon is less conductive than the iron. So it takes less heat to get a cast iron pan very hot, very quickly (they are fuel conservative). A high carbon content also makes them very hard. This means they have a low friction surface (so they require less lubricant) and they resist permanent surface deformation (scratching). These are the reasons why something like a cast iron pan is made of this iron with a ridiculously high percentage of carbon in it by weight. Because it's made for heat applications (cooking low fusible point metal casting etc). However, cast iron is also very brittle. Hardness and toughness are not the same thing. They are mutually exclusive to some degree. You can make something harder (resistance to permanent surface deformation; Like scratches and dents). Or you can make it tougher (resistance to self separation; like chips and cracks). But generally when you make something harder you make it less tough. When you make it tougher you make it less hard. So with this foreknowledge about how all that works in place we can now think about this logically. Would it make sense to make a pestle and mortar out of a material that is brittle and better suited for high heat applications? The obvious answer is "No". You'd want it to be made out of something softer. High/medium/low carbon steel as well as wrought/ductile iron are all better options. Now there are different grades of cast iron. So it's possible that it's just on the edge. A little higher than the highest carbon content crucible steel . But a little lower then what would be used for cooking. So we can reason that this is obviously on iron product. But likely not the same grade of iron as the cast iron used on say a Wagner skillet. That's what can be discerned about the composition without handling the piece in person and doing some tests. What test would I do to narrow it down? About the only reliable one. A spark test. This is fairly non-destructive (although it would leave marks). And it works basically by touching some part (obviously a part that isn't going to be visible on display) with a grinder. The spark shower, shape, spread, arc, and color can inform one as to what the composition is with high precision. In case you are interested in knowing how to do this test yourself for narrowing down that composition (it's not hard) here is a link to a PDF on the subject: Metal Identification Now onto application. Again we can reason this out. This is extreme overkill for pounding out some flour or meal in my estimation. You've a much harder and heavier set of materials than is any where near necessary to efficiently grind grain. This seems more on the order of what is used to crush pigment minerals for paints and dyes. Or Borax and alum crystals for flux and fixants. Or Limestone to be baked into quicklime. Or large salts for glazing. This seems like it would fit better around a dry salter's (someone who makes inks and dyes) or a potter's setup. Even a small foundry more so than a kitchen. Regarding construction I would say that the mortar definitely looks cast. the dot and line on it is a classic Sprue and seam mark. We even see scoured marks going against that grain. Indicating that there was left over scales/scabs which needed to be chiseled off. On either the mortar or the ball you can see the striations in the grain pattern that even indicate direction of molten flow. The ball seems to have a large sprue mark (perhaps two?). But on the ball there is that interesting smaller bit that looks squarish. That could very well be a pin that in part secures the ball to the shaft. So the peen at the end would keep the ball from falling off the shaft and the pin would keep it from moving up the shaft or turning on the shaft (if it is indeed a pin). The shaft is definitely not cast. But manually hammering out a nice round round like that is fairly difficult and time consuming. Likely it was extruded and then drop forged. Which is basically where the smith has a die that the piece is suspended over. And the piece would be moved and rotated against the die as a large hammer is lifted and dropped (not driven with force but let to fall under it's own weight) onto the piece causing it to conform to the shape of the die. I wouldn't doubt it even if the rims of the mortar got a few turns against a drop forging die post-cast. I've not seen a pestle and mortar quite like this before. I've seen ones this large and even larger. But those are invariably made of wood. I don't think this was a mass produced thing. This has the appearance of having been made in a workshop for a specific purpose. I couldn't even begin to speculate on a date. The processes that would have gone into making this have been around in Europe at least since the middle ages. There isn't anything definitive in evident process that would nail it down precisely as to place or time of origin. I hope what I have laid out here was not too much of a bore to read through and that it is at least somewhat helpful. [Edit: the seam is not an indication that the mortar was made in two halves. Just that it was a two part mold for a single piece and the seam with it's sprue is simply where the mold would have been opened.closed at. Check the bottom of the mortar for another sprue mark (this will give an indication of mold orientation)]. [Edit 2: The 8 mark is likely a missed/skipped blow from a setter. That is what looks to be the exit hole of what I believe to be the pin I referred to earlier and it would have been peened there. If there were a makers mark it would likely be on the bottom of the mortar].