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Mortarium - M. Demetrius - 02-20-2009
First of all, I freely admit that I am a totally terrible potter. I have trouble telling when the clay is right for working, when it should be left alone, and when to stop fiddling with it. I can tell when it's too wet, though, because there's as much on my hands as there is on the table. :lol:
My wife has been trying to figure out a niche she can fill in the hobby, and although we've had some very difficult times for lots of reasons in the last couple of years, we've managed to hang on through the various assaults we've encountered. She had a debilitating and disabling episode with two strokes a couple of years ago, and has pretty much lost the ability to do much with her left hand (harder to spin and weave nowadays). So many of the things she used to do aren't available. She wants to make Roman cosmetics and perfumes, and we're working on that project. It involved grinding all sorts of strange plant leaves and roots, and various rocks and mineral derivatives, some things I've never heard of, and a few that I have, putting them in different oil, wax, wine, and vinegar suspensions and so forth.
Please, potters, don't take this the wrong way, I wish I could afford to buy things, but for the time being I just have to do things myself, or do without. I do not in any way cast anything negative your way about your pricing. I marvel that what you do is even possible.
We needed a grinder. We only had a little bitty white porcelain one, which is about 2 millennia out of time. Couldn't see paying the price a real potter charges, not that it's too high (don't slap me, potters), just that we didn't have the money at this time. So, being the stubborn man that I am, I decided there has to be a way for a non-potter to make pottery anyway, and a mortarium is basically a bowl. This will be the progress report on the venture.
This is what we're trying to reproduce, the specimen shown is from the Museum of London, found on the web, and is pretty typical of the run of the mill household food/herb grinder.
Re: Mortarium - M. Demetrius - 02-20-2009
I am totally sure that these should be made on a wheel. I even found an image of someone doing just that. I don't have a wheel, or the knowledge to raise a bowl out of a lump of spinning clay. I have seen it done, and I'm convinced it's just magic. They seem to know the right incantation, and upcomes a bowl, a vase, a bottle. I just get my hands dirty and have a puzzled look on my face. I don't know the potter in this picture. It came from Google.
http://i223.photobucket.com/albums/dd29 ... elmade.jpg
All right. I still needed a mortarium. I took a copper plate I bought from a junk store, and put a dish in the middle, just like making a shallow shield boss. Then I added a depression around the edge, sort of like a little trough, to make the raised ridge on the mortarium. Made a spout and continued the ridge out to the edge.
I trimmed the copper down to the shape of the outside margin of the desired size. I still need to go back and smooth out that ridge bit. It's pretty rough. I need this thing fired a week from day after tomorrow. The first ones will be rough (unless they explode in the pit firing, then they'll be driveway filler) but they should work. Rough isn't so bad, for right now.
Facts:
1. Wet clay sticks to copper really well. A release agent is needed. Clay formed against dry copper will only come off in quite a few pieces. Proven.
2. Olive oil doesn't do the job. Proven.
3. Talcum powder works a little better, but it's still hard to get the bowl part free, and the clay suffers for all the handling. Proven.
4. I'm speculating that heating the metal and waxing it will be an improvement. Logic says so, but that doesn't mean much. Not proven yet.
I have had a little success so far. Here's some pictures.
http://i223.photobucket.com/albums/dd29 ... hetool.jpg
http://i223.photobucket.com/albums/dd29 ... rtaria.jpg
Report continues.
Re: Mortarium - Salvianus - 02-21-2009
Thanks for posting your ideas and innovative method: so cunning you could stick a tail on it and call it a weasel
Keep us posted!I'm deliberating pestle designs myself right now - some older sources just say we don't have any because (or possibly therefore!) they were made of wood. The bronze 'cosmetic pestle' seems to be a different species.
Re: Mortarium - M. Demetrius - 02-21-2009
Wood is a good choice, I agree. Seems to me there would be no easy way to keep the clay out of what you're grinding. Clay against clay...
A passable release has been discovered. I heated the copper form and rubbed candle wax over it. Touched it a little soon, and put it right back on the stover burner. :roll:
When it was cool, I buffed it up a little with a dry cloth, dusted it with talc, and the slab of clay with talc. Came out pretty easily. But, the talc sucked up a lot of water from the surface, and it was harder to work on the upside of it. That's ok, it came out of there without a lot of fuss.
So far, three off the form, and two sent back to the clay bucket. Nothing much new to report but that so far. The proof will be in the firing. Yikes. :|
After the event this next weekend, I plan to do some remodeling on the groove. It needs to be smoother, and sharper at the bottom. This will make it easier to remove, and perhaps require less fixing up. Slightly encouraged, I am now determined to get two pretty nice ones before moving on to something else, unless I run out of clay first.
Re: Mortarium - Sutoris - 02-22-2009
Have you tried vaselin?
Making little clay molds for pewter casting I
always put a little coat of vaselin on the object.
Filip
Re: Mortarium - M. Demetrius - 02-22-2009
I'll bet that would work. I suppose another choice would be to carve the form in soapstone. Not much sticks to that, either.
Re: Mortarium - Robert - 02-22-2009
If you can carve the mold from soapstone, perhaps you can also pick up a piece of tuffstone at a garden center and carve a depression in that. This would also be good for grinding pigments and things. Just a thought. Good luck with your project, hope the firing goes well.
Re: Mortarium - Matt Lukes - 02-25-2009
The problem with some release agents is that you might encounter problems firing the clay after- vaseline is a petroleum byproduct so would not be a good choice I think since it'd certainly burn. Have you tried letting the clay dry in place on the metal? I can't imagine it'd still stick once it's not so wet since it's almost certianly the water that's causing the adhesion (thin film adhesion)
The other option is to make a plaster mould and that's no problem with clay since it draws water out and makes the clay very easy to remove in a nice, solid form relatively quickly (how oil lamps are made).
And the maker mark is easy too- shape a lump of clay to the edge of one of your unmarked pieces, let it dry, and scratch in the letters or whatever you want to be raised and voila :mrgreen:
Re: Mortarium - M. Demetrius - 02-25-2009
Well, the vaseline would burn off all right. It might leave some discoloration, but since these are being pit fired, it wouldn't matter, really. So far, the wax on the metal, and talc on the clay is working just fine.
Yes, I let the first one dry overnight. Problem with that is that the clay shrinks when it dries, and the metal doesn't. After I saw it cracked into several pieces, I realized what had happened. Sort of like mud that dries out and makes reticulated broken bits...actually its a whole lot like that. :? Anyway, the pieces lifted off the metal easily enough, but I was sort of hoping for just one piece.
I did think about a clay mark tool, and that's probably about the easiest way, you're quite right. If I slipped it in the fire pit, it would last until I dropped it on a hard surface, or lost it, I think. Might as well make several, if I make one. Won't add that much time or trouble. I fire the 3 mortaria and 2 pistillia on Friday, plus three stamped clay floor tiles I made a week or so ago. I'll know by Saturday if anything survives. I'll cross my eyes for luck. 8)
The tiles
http://i223.photobucket.com/albums/dd29 ... nboard.jpg
Re: Mortarium - Sutoris - 02-25-2009
Quote: Have you tried letting the clay dry in place on the metal? I can't imagine it'd still stick once it's not so wet since it's almost certianly the water that's causing the adhesion (thin film adhesion)Matt,
That only works good when you put clay in a mould.
The shrinkage will do the job.
David,
love the mark on the tiles, you gonna use them as bussiness-card
Re: Mortarium - M. Demetrius - 02-25-2009
Probably not business cards, as they are pretty heavy. :lol: But they might make a nice paper weight. Version 1.1 will be cooler, with the boar stamp.
Re: Mortarium - M. Demetrius - 02-28-2009
I had hoped to pit fire the mortaria, pistillia and tiles this Saturday, Feb 28, but it has been so dry for a while here, drought, that the fire department has said NO outside fires at all. Might be a while before I can do that after all. You see, the Fire Chief lives right across the road from me, and it's not worth risking a) a wildfire breaking out in a residential subdivision, or b) getting fined 500USD, plus they flood the pit with water, shattering all the hot pottery.
When fired, I promise to post pictures, if any survive the firing.
Re: Mortarium - Matt Lukes - 03-09-2009
Right, okay, I should have clarified- dry a BIT... hence '...once it's not so wet'. :mrgreen:
Re: Mortarium - M. Demetrius - 03-10-2009
Talc works. And when the clay is completely dry, almost all of it dusts off the surface, and I suspect the rest will burn away during firing. Got the lot of the mortaria and the tiles over to a real potter to bisque fire them. Any survivors will someday be pit fired to give them that rich color that they deserve.
No word back yet about the firing. Got my eyes crossed for luck... :roll:
Re: Mortarium - Lugorix - 03-11-2009
Maybe I missed it somewhere above, but did you add the grit on the inside before firing? It's what makes it a mortarium instead of just another ceramic bowl. I highly recommend find a copy of Roman pottery in Britain by Paul Tyers if you haven't already. I think you'll benefit from his drawings and discussion. Photos from museums just don't show the complexity of these little masterpieces.