Wednesday, October 21, 2015

Do the Math

Me, in class, explaining all this last night.

A friend of mine has often give me this good advice: Don't guess at anything, if you can help it.

I get the advice often, because I tend to forget it: eyeballing and seat-of-the-pants are much more my natural style. So when I had a request for 20 ounce mugs - and they had to be pretty-damn-close to 20 ounces, not "20-ounces, give-or-take," my first thought was to make a few mugs that looked like they would shrink to about the right size, write on the bottoms what the wet dimensions were, and see which one worked out best, and proceed from there. That approach will get the job done,  but maybe there is a better way?

Enter arithmetic! Or maybe this is algebra? Actually it's geometry, but it is algebraic geometry...? Or arithmetic geometry...?(OOPS SORRY, DERAIL. Back on track now.)  All of the necessary information to tell me how large this mug has to be is available.

Q: Okay, Google: How many cubic inches is 20 ounces of water?
A: 36.1 cubic inches
So far, so good. Now, so I need to make a mug with an interior space that will shrink to 36.1 cubic inches, plus a little so the liquid is not right up to the brim. How might one do that? Well, starting simply, the equation to determine the volume of a cylinder is
π r2(H) = V
where "H" is the height, and V the volume. Now let's put in the numbers that we know. Well, π is 3.141etc, etc. V is 36, plus a little, right? Plus how much? If I want a half-inch of space between the rim and the liquid, that number is 3.5 (which I arrived at by doing the above equation, but skipped that part so I wouldn't be repeating myself.) So, let's put in 39.6 for "V". To get the radius, we need to decide on a diameter, and after measuring a couple of mugs of different sizes, I decided on 3 inches - doesn't sound like much but is actually a pretty wide mug. That makes the radius 1.5. One-point-five squared is 2.25, so now we have all the numbers except one, H; this is the number our equation will give us. Like this:
3.141 x 2.25 x H = 39.6
Now we need to cancel out some of those numbers. We could say the same thing like this:
3.141 x H = 39.6 ÷ 2.25
...which equals 17.6. So now we've got
3.141 x H = 17.6
Cancelling out the π, now it looks like this:
H = 17.6  ÷ 3.141, which equals 5.6 and some change.
So our mug (assuming it was a perfect cylinder, which it's not, but we'll get to that) should, after firing, measure 5.6" tall by 3" in diameter; that's the interior space, 'cause that's where your coffee goes. On the interior. Usually. On a good day. So while I can easily measure the interior diameter with calipers, I'll need to tack on 1/8 inch in height for the bottom, and the clay that stays on the wheel.

My claybody shrinks something like 13%, but that is plus or minus 2%; and these mugs really shouldn't be too large, but they absolutely cannot be too small, so I'm gonna assume 15% shrinkage. (Also makes the math easier to do in my head, when I need to.) So now we have wet dimensions of 6.5 (adding the 1/8 inch and rounding down a hair) by 3.5 - again with a slight round up of .05 inches. 

Well, now we're cooking! If I start with this cylinder, and then add some curves, if I am careful to curve in at one spot about the same amount as I curve out at another, I should still arrive at my 20 ounce capacity. I will be guessing - let's say estimating, sounds nicer - how much clay to use, and then if it doesn't feel right - too clunky, too flimsy - adjusting up or down. I don't mind that, because that only takes a few minutes to work out, as opposed to having to wait a whole firing cycle. 
I am going with 1.75 pounds of clay. These mugs will be in a restaurant setting, so will be frequently washed, and will mostly serve beer, so users may be less than dainty with them. I am thinking a little thicker than usual might do well. On the other hand, I don't want a behemoth, since 20 ounces of beer is a little weighty all by itself (weighs exactly 20 ounces, in fact!) so I am only going a tiny bit thicker than usual. 

I wish I could make these mugs today, but alas, I have to go pile brick on  top of one another: I've promised myself the stack will be finished today so that weight - all 1000+ pounds of it - will be off my mind. And when it's done I will enjoy another kind of pie, as a reward. 

Yay math.  

Friday, October 16, 2015

What's Up

Foliage is late this year here in Maine, but incredibly beautiful. I had a good chance to see it as the sun was setting yesterday, while I limped my car home at 15 miles per hour on Rte. 201 through Topsham, Bowdoinham, and Gardiner. Beautiful! My favorites are the peachy maples, especially when they still have some green, or are right besides the flaming red ones.

Oh, what's that? I buried the lede? I guess I did, but I thought that anything - even a gushing foliage review - would be more interesting than another story of my car maladies.

Yeah, my car has issues again, which caused me to miss my evening class - Week 1, at that. Sorry, beginners! But the ever-capable Karen Dyer Dicenso jumped in for me. VIP Auto has the vehicle, will find out later today what's up with that. Whatever it is is bound to be spendy - the best I can hope for is "not over my credit card limit."

But, better things are coming:
  • First Friday! Portland Pottery is hosting an opening for Faculty and Staff during Portland's November First Friday event. That's November 6, from 5-8.
  • The Central Maine Clay Artists group have chosen our location for the Holiday Pottery Shop! This is the tenth year, and the shop has come full circle: 100 Water Street, Hallowell is where the group held its first meeting in 2005. We hope to open in by mid-November.

  • The stack is half rebuilt. I am taking it easy, doing just a few courses a day, to avoid dinging up my elbow, which didn't like the repetitive motion involved in taking all those brick down.
 Aaand, just had a call from the mechanic, saying they don't know what it is but it's going to be expensive. Well, that's not exactly what he said, but close enough.

Sunday, October 4, 2015

Screamy Feet

Ugh, this GETTING OLD thing! Amirite?

I'm on my feet a lot. Throwing days are mostly sit-down, of course, but decorating, glazing, loading, firing, packing, pricing, teaching classes - basically every work activity other than throwing (or blogging!) - is a standing one. For months now I've been literally hobbling when I wake up in the morning, barely able to put weight on either of my feet. It loosens up after a few excruciating minutes, and then I am able to walk normally, but then starts hurting again in the early afternoon. If I still down for any length of time, I go through the morning limping routine all over again. Turns out that what I had been calling "Screamy Feet" has a more official name: Plantar fasciitis

But for every curse, there is a blessing,* and right around the same time I started falling apart, I was able to get health insurance. So I told my doc about this foot problem, and she had a great suggestion:
  • fill a two-liter bottle with water
  • freeze it
  • in the evening, when reading or watching netflix or working online, place your feet on it like a little footstool. 

This ices the injured fascia and reduces the swelling. After one treatment, I was amazed at the improvement: no limping at all this morning. We'll see how it holds up over the course of the day.
In other news:
  • Still in the throwing/decorating part of the making cycle; I expect to fire a bisque in about two week, and a glaze about a week after that. 
  • It's already time to talk about the Holiday Pottery Shop! Fellow potter Mary Kay Spencer, Barb Loken and I checked out a space in Hallowell this week - the big red building on the north end of downtown, for my local readers. Still a couple of details that need to be nailed down but I am optimistic about this space. If it doesn't work, there are possibilities in Gardiner or Augusta, but we seem to do best in Hallowell, so we look there first. 
  • Soda firing workshop at Watershed next week! Still a few spaces - give Portland Pottery a call if you're interested: 207-772-4334. We'll glaze and load on Saturday, fire Sunday. Bring two cubic feet of bisqued work, I'll bring slips, glazes, and wax. $125
  • Putting the pottery stairs out front of my house one last time for the season. It's a bright sunny weekend, if a little cold; hoping to catch a few late-season bargain hunters.

 *HAHA as if