I am so delighted to have a few of my bird jars in this juried exhibition at the True North Gallery in South Hampton, Ma. from June 19 through September 4, 2010. Read about it here through the True North Gallery blog
http://truenorthgallery.net/blog/
Last week I finally decided it was time to donate a good portion of my hair to Locks of Love. I was fortunate to have the kind of hair capable of cutting off circulation around your toes when a stray got into your sock and when it was worn down strangers in the vicinity would succumb to its firm tangled grasp by means of static electricity. Suffice to say it was long enough measuring in at 44 inches in length. Oddly, I never really realized just how long it was until I cut it.
I proudly made my meager sacrifice and settled on donating 21 inches to Locks of Love. My head feels 10 pounds lighter and I can actually wear it down now without risk of injury to myself or others.
If you're like me you probably end up with a fair amount of scrap clay and slurry by the time you finish making pots. Reclaiming those scraps is a simple process that requires just a little bit of time.
Materials needed: a 5 gallon plastic bucket and lid, a plaster block, a turkey baster and a ladle.
For the plaster block purchase 25 pounds of pottery plaster or regular plaster from a hardware store. Follow the mixing ratios and directions designated for that particular type of plaster. Whatever dry plaster is left over you can store in a lidded bucket, make sure to save the ratio and directions before throwing away the bag, been there, done that. When handling dry plaster always wear a respirator.
There are many ways to create a plaster mold. An adequately sized mold for the home potter is a USPS flat rate box, free from the post office. Cut off the top of the box and cover all the corners and seams inside and out with duct tape. Working on a level surface, take a board as wide as the box and cover it with a thick layer of newspaper. Place the USPS box on top of the board and pour in the plaster leaving 1/2 to 1 inch headroom. Gently lift and drop the board under the mold to tap the air bubbles in the plaster to the surface. Allow the plaster to set up overnight before removing the cardboard box. Now you can take a scraping tool to carefully clean up the sharp edges. Don't worry about the cardboard that sticks you can get that later. Place your new plaster block in a well ventilated area with a lattice underneath so the air can move around it. Two 2" X 4" will suffice. Let the block dry for 1 1/2 to 2 weeks. Using a damp green scouring pad refine the pores of the plaster block with a little bit of elbow grease. The green scrubby will also remove the remaining cardboard from the surface. Place your block on top of two 1 inch furring strips or the like for constant ventilation and to prevent mold growth. I designate one side of my plaster block for white clay and the other for red clay.
Now the fun part, processing reclaim.
Step 1- Designate a 5 gallon bucket with lid to one type of clay for reclaim (cone 02 red terracotta clay)
Step 2- Add all red terracotta clay slurry from the wheel and slurry water containers to the recycle bucket.
Step 3- Completely dry all large clay scraps before slaking them down in the recycle bucket (this will allow a more uniform slurry).
Step 4- Allow the clay and water to separate overnight. The heavier clay particles will sink to the bottom.
Step 5- Using a ladle, gently scoop out as much water as you can. With a turkey baster you can suction off the remaining 1/2 inch of free standing water if you so choose.
Step 6- Carry your bucket to the plaster block and give it a good stir. Using one hand, repeatedly scoop out as much clay slurry as your block can handle before pouring off the sides and making a mess.
Step 7- Wait. Depending on the humidity in the air it may take up to 2 days before your clay is firm enough to lift off the plaster block.
*Here you can either continue recycling or wedge your clay for reuse.
Step 8-Wedging up your reclaim, roll the clay out into thick coils of even thickness.
Step 9- Using your coils, create a framework around the plaster block. Make certain to secure the coils to the base of the block on the inside, outside, and joints.
Step 10- Fill the coil framework with clay slurry.
By creating a coil frame you can recycle more clay at one time. As the slurry dries it will sink from the edges of the coil frame, simply push the top edges into the slurry to keep them moist. When the slurry is firm enough, pull it away from the plaster and wedge it up for reuse or store in a lidded plastic bucket to keep it moist for the future.
NOTE- Never use a sharp scraper to remove the clay from the plaster block. Plaster and clay do not mix. If it does, the plaster will pop in the kiln leaving behind pitted pottery and ruined work.
In anticipation for the 2009 toad and frog house season, I spent and afternoon creating a charming animated short on how a toad finds a home. Perhaps toads don't really have newspapers, real estate, VW beetles, banks or use snails for currency but it certainly is an amusing tale.
On my most recent trip to my local ceramic supply store I splurged and purchased a Kemper Klay Gun Tool. It wasn't a huge expense, only $14.00 USD and the amount of time the Klay Gun tool would save me was well worth the investment. I needed a small extruder for making the vines on my ceramic garden toad houses. I was filled with excitement over my new Kemper tool and could hardly wait to try it out.
Now, before I made my purchase I googled for reviews on the Klay Gun Tool and could not find any. I have a great many Kemper tools in my studio and they have provided me with many years of hard abuse. This tool however, was a disappointment. The steel is the poorest quality, the kind that will rust if one accidently breathes upon it. The mold edgings were sharp and the 3/4 of the dies would not fit into the Klay Gun cap. Not to mention that the cap would not even thread due to the rough edging.
One benefit to using cheap metal is that it is easy to hand sand. After 2 hours of sanding the burrs and the dies of this tool I finally modified it enough to make it work as it was intended. Thus far, I am content with it's use but I seriously question whether or not it will stand up to the test of time. I feel that cross threading will be its ultimate demise.
So, depending on how much you value your time will relate directly to whether or not you want to purchase this tool. I figure this Klay Gun has cost me about $50.00 excluding the cost of sand paper and travel time. And by the way, don't bother emailing Kemper about your complaints, they make it a point not to respond. Will I purchase from Kemper in the future? Well, yes, but only the tools I know that are reliable. The bigger question is why do we allow companies to sell us sub par products that require modification in the first place? I know I spend a good amount of time fixing the new products I purchase from stores today, what about you?
For years I have been using a fine tipped glaze bottle for my slip application and decorations. For just as long I have been immensely frustrated when the tip gets blocked and expels a giant blob of clay slurry all over my design in 30 second intervals. Of course, it's my own fault for putting up with it as long as I have as well as forgetting to purchase a slip bottle when I am at my ceramic supply store.
Just the other day the heaven's were singing when I spied a near empty Elmer's glue bottle in the closet. The light bulb above my head signaled that this container would make a good slip bottle. I rigorously cleaned the container with hot water, my small sponge on a stick tool and a hooked wire to clean the difficult top edging. I also removed the orange plastic top and cut off the inverted "Y" white plastic tip to permit more slip flow. Taking a small drill bit I enlarged the opening of the orange cap from the underside out. Mixed up a nice smooth red clay slurry, filled the Elmer's glue container by way of a funnel, closed it up and squeezed to my hearts delight. No more giant slurry blobs on my designs or toads. My toad house production is going to get a lot easier now.
The only question is how to keep the slurry in the container from drying out since I removed the inverted "Y"? I decided to pour in 1/2 inch of water to keep the slurry moist and found a thin piece of copper wire to set in the hole. The sitting water will not mix with the slurry so long as I don't vigorously shake the container and a fair amount of the water can be squeezed out before the next use.
This is a really good question and one that you will often hear from customers wanting to buy your functional pottery. Fortunately, there are a lot of tried and true glazes available out there but that doesn't necessarily mean that they will be safe with your clay. In order to have absolute certainty I recommend having your clay and glazes professionally tested which can be a costly affair but if you are selling functional dinnerware to the public, it's a safe investment.
Concerning our native clay, I have covered the shrinkage rates as well as the rate of absorption in my previous postings. Now we want to test for the absorption rate of your clay and glaze. In order to do this you need to completely glaze your test tiles and fire to maturing temperature in the kiln. In the realm of earthenware clay your bisque firing temperature is normally 1 to 2 cones hotter than the glaze firing temperature.
After completion of the glaze firing we will again measure our 100mm lines and weigh the tiles. The final lengths of the tiles will determine our overall shrinkage rate from dry to glaze for our native clay. Again, under 15% is good. Next you will need to boil the glazed test tiles in water for 1 hour. Safely remove the tiles from the hot water and allow them to cool to the touch before weighing them again. The difference and average of dry glazed test tiles to the saturated glazed tiles will allow us to determine the rate of absorption of our clay and glaze. If your percentage averages out below 3% you have a good clay and glaze fit. Chances are very good that this clay and glaze is food and water safe. Higher percentages will result in weeping water as well as wares that are unsanitary.
A final test involves acidity. Take one test tile and soak it in vinegar or lemon juice for 24 hours. If the glaze is discolored and showing craze lines your glaze is not safe for acidic foods.
If you happen to have a poor clay and glaze fit you can still create wares that are not crafted for food and drink as well as test with other glazes.
Upon completion of the bisque firing you will again weigh each tile as well as measure the lengths of the 100mm line. Using averages you deduce the shrinkage rate of the native clay from wet to bisque. Example, all tiles A- E began with a 100 mm. After the bisque firing to cone 05, Tile A measured 92mm, B- 92mm, C-95mm, D-95mm, E- 96mm. Differences being 8mm, 8mm, 5mm, 5mm and 4mm. Therefore, to reach the average will will add these numbers and divide by the total number of tiles. 8+8+5+5+4=30mm divided by 5=6% shrinkage rate from wet- bisque. You can also go further with the data you have collected and deduce the average shrinkage rates from wet to dry, wet to bisque, and/or dry to bisque. An average shrinkage rate under 15% will make a good clay body for continued testing.
The next test we will do is for lime blowing. In firing clay above 1632 degrees Fahrenheit calcium carbonate decomposes into lime. Clays with an excessive amount of lime or calcium carbonate will cause problems in the future. As the clay absorbs moisture from the air the lime inside will expand causing pieces of the clay to flake off. Lime is easily recognized by small pits and a white or yellowish film on the surface of the pots. There are remedies one can do to correct problematic lime blowing such as firing at lower temps or firing in a reduction atmosphere. For the lime blowing test, soak your bisque fired test tiles in distilled water for an hour and allow them to dry for a few days. If lime is present you will see a film form on the surface of the tiles.
Without certainty I believe that lime is causing a problem in this 180 year old house that I reside in. The red brick chimney we have is mortared in place and probably dates back to it's origins. Due to a slow leakage around the flashing of the chimney it might be possible that the brick has too much lime or perhaps the mortar has slowly leached into the brick causing large chunks and flakes to fall off.
The rate of absorption for the bisque clay will tell us how well the clay will absorb the wet glaze. For this test we rely on the weight measurements we have been taking. Boil your bisque test tiles in water for 2 hours. With tongs safely remove the tiles from the boiling water and allow them to cool to the touch on a dry towel. With your triple beam or digital scale take a weight measurement for each saturated test tile. The difference and average between the dry bisque and saturated bisque tiles will provide us with our rate of absorption. A percentage higher than 10% will provide a good absorption rate. Percentages under 10% will make it difficult for the bisque to absorb the glaze. If such is the case you can bisque at a lower temperature, cone 06 or cone 07, or heat the pots before glazing. Having a good rate of absorption with your bisque fired clay makes it easier to get a even coat of glaze on your vessels which will provide a uniform glaze coloring as well as a good clay and glaze interface.
To quote Michael Cardew from his fantastic book, Pioneer Pottery,"An unknown clay should be presumed guilty until proven innocent." Commercially available clays often have the shrinkage, porosity and absorption rates listed in there catalogs, the work has already been done. But what about a unknown native clay?
In the near future my husband and I will be moving to our property in western New York state. Our parcel is filled with native terracotta clay and shale. As a potter this is a potential gold mine for me but I don't know much regarding this particular clay body. Is this a clay body I can use for throwing on the wheel, what temperature does it fire to? One thing I am certain of is that there were local potteries in the old days so chances are pretty good that I can utilize this clay.
After finding a nice pure vein of clay I was able to do a simple plasticity test by rolling out a wet coil and checking for cracks, it passed. Refer to my previous post- "Native clay processing on a large scale". My next step was to make a couple of small balls and bisque fire them in my kiln to cone 05. I fired these small balls of native clay inside a commercial clay bisque fired bowl as a precaution. I did not want the clay to melt and ruin my shelving, I could sacrifice the bowl. The clay survived and fired to the same rich red coloring as my commercial terracotta clay body. Now it's time for some more testing.
To test the shrinkage rate of a native clay works on averages and does not involve complex formulas, thankfully. To take from Tom Buck, Leon Nigrosh and Michael Cardew begin by rolling out a slab of native clay that is 1 cm thick. Allow the slab to set up for a few hours before cutting out your test tiles. Take a piece of box board and cut a rectangle 13 cm long and 4 cm wide. This box board will be your template for the tiles. Using a fettling knife cut out as many tiles as you can, preferably 10. Next draw a line 10 cm long down the middle of each test tile. Set them aside to stiffen up to the point of handling.
Thinking ahead to porosity and absorption testing were going to kill 2 birds with one stone. Label each test tile A, B, C, D and so on. Using a triple beam or digital scale weigh each tile in grams in it's wet state and write it down, always keep notes. Completely dry the tiles flipping as needed and/ or weighting them to prevent warpage. After the tiles have completely dried, measure the 10 cm lines (100 mm) and weigh them again. Example- Tile A is 96 mm (-4 mm), Tile B is 97 mm (-3 mm), Tile C is 95 mm (-5 mm). The average difference of A+B+C+D+E+F+G+H+I+J =X divided by the number of tiles equals your wet to dry shrinkage in percentage. Example- in mm- 4+3+2+3+4+3+2+3+4+3= 31 divided by 10 = 3.1% wet to dry shrinkage.
Next we are going to fire the test tiles in the kiln to bisque temperature, cone 05 or cone 04. After the kiln has cooled and you have removed your tiles measure each 10 cm line again and weigh the tiles again. Tile A is 89 mm (-11 mm), Tile B is 90 mm (-10 mm). Again, take those averages and divide by the number of tiles. This percentage will give you the average wet to bisque shrinkage rate. Somewhere in the range of 10- 15% is good and worth investing the extra time for glaze firing and absorption and porosity testing which will be part of my next post.
