Sara78 reacted to glazenerd in Re-Using Frozen Clay
Freeze dried might be a better description. I can see granulation in the large crack on the right: one sign of frozen clay. However, the moisture content of this clay is low: would guess around 5%; which also causes cracking and splitting. In essence, it is losing its plasticity from both issues. Need to hydrate back to the 9-10% range. You have it slab rolled out; spritz it with a spray bottle, fold over, roll again.. repeat...until it rolls without cracking.
Sara78 reacted to Min in Best Approach To Obtain Solid Blocks
I like your #3 option of slipcasting but not leaving it solid, then firing on coils, waster piece and/or grog. I think you will have less chance of warping with slipcasting than using slabs or hollowing out a form. If is has to be solid looking then maybe you could add a base to a slip cast piece after it has been removed from the mold.
Sara78 reacted to Magnolia Mud Research in Best Approach To Obtain Solid Blocks
My design approach for a solid block approach would be one or both of the two options:
Option 1. Make the piece out of paper clay using dried 'blocks' of paper clay and paper clay 'mortar' to assemble the blocks. After this was dried and bisqued, I would add a thin layer of paper clay and thinner layer of slip to produce a smooth surface layer.
Option 2. Use the one of the clay bodies designed by Jerry Rothman or Fred Olsen that they used for their big sculptures. These clay bodies have very little shrinkage and their pieces are also thick. Rothman's clay was available from Aardvark several years ago. If you called Fred Olsen, I am sure he would give you some advice on the clay body choices.
More generally re the project:
Approach the problem by continuing to ask the kinds of questions you are doing, just go deeper into the requirements that the clay body (really the ceramic materials) must meet for final piece to be successful.
From what has been revealed so far, I think you need a clay body that is solid, but possibly porous, that is dimensionally stable, dries uniformly in a reasonably short time, fires in a reasonably short time. Does product need to be fully vitrified? Think brick clay instead of tea cup porcelain. Does it need to fired at all? What about surface treatments? Glaze, stain, paint, color, texture, gloss, etc.?
Could the project be made by making thin fired layers that are 'glued' together to produce the overall shape? I once made a ceramic sphere that way.
Sara78 reacted to Pres in Best Approach To Obtain Solid Blocks
Test a batch of clay with 75-80% grog, then use a slip or glaze on the outside. This is the only way I could imagine you doing a "solid" block. Otherwise take the routes others have given you of cutting and hollowing, or slab building with thick slabs. Wooden forms would definitely help with the second technique in case you decided to use slabs.
Sara78 reacted to Dick White in Best Approach To Obtain Solid Blocks
You are going to have problems firing any ceramic that thick. It is possible, but requires a long slow firing of at least 2 days. The problem is not only the drying of physical water to eliminate explosions from the phase change to steam at 100C, but also a chemical change in the ceramic that creates more water at around 450C-600C.
You are aware of the problem of the the clay form exploding if the interior is not completely dry. A solid block of the thickness you describe will likely not dry by itself just sitting in the open atmosphere. Rather, you will need to gently heat it in the kiln at 90C, just below the boiling point for water, for a very long time until the heat has penetrated through the entire block and evaporated all the remaining water. A point to remember is that as the water turns to vapor, it will leave the surface from which it evaporated cooler, so while you are heating it, it is simultaneously cooling itself by evaporation. It will take a long time for that moisture and water vapor to work its way out.
A second vulnerable period for clay is less understood. The theoretical chemical formula for clay is Al2 Si2 O5 (OH)4, or reordered to Al2O3 2SiO2 2H2O - which is one molecule of standard alumina oxide, 2 molecules of standard silica oxide, and 2 molecules of standard water. At red heat, the molecular bonds between the alumina, silica, and hydroxyls break and the clay reforms into ceramic of just alumina and silica oxides and the hydroxyls are released, forming into more free water. This water is already gaseous so you won't have a steam explosion as before, but the water vapor must get out. The ceramic body will have open pores at the lower end of the temperature range for this phenomena, and the vapor will escape without harm. However, if the piece is very thick, there will be a significant temperature differential between the surface and the deepest interior, and the pores on the hotter surface will begin to close, sealing the escape route for the newly formed water from the interior. The result will be a spalling of the surface of the ceramic. Large chunks of the surface will just break off. The only way to avoid this is a very long firing with a very slow rate of temperature increase.
Sara78 reacted to Marcia Selsor in Best Approach To Obtain Solid Blocks
Build it solid , then cut it open and carve out the inside, put it back together and most definitely leave a pinhole for the air to escape. I would dry it and then dry it in the kiln. Rotate it to allow all sides to dry. And I would fire it up on some coils to allow any steam still in it to escape.
Sara78 reacted to LeeU in Best Approach To Obtain Solid Blocks
In my own work I like quite heavy pieces and solid pieces...the biggest solids I've done are about 3.5 sq. I dry the heck out of them, single fired to ^6. No problems so far, but I am not well-versed in the pit falls as I "use" flaws and accept mishaps in my approach. If the body is well-wedged the surface will be very smooth--if I don't do a thorough wedge, I will get cracks/texture/holes (no explosions!) but I aim for that effect ahead of time.
Sara78 reacted to douglas in Wedging Clay
As a beginner, go ahead and learn to wedge so you can do it when you need to.
But no, it is never absolutely necessary to wedge your clay. However, it is a lot easier to throw properly wedged clay than clay with air bubbles, or chunks of dry clay from reclaim mixed in.
Sara78 reacted to Mark C. in How Is Made
The round form is two pice the cone inside is a plug-with a drain hole -my best guess.
If you want 10,000 of them send the master form to a master mold maker and ask for the rubber working mold casts. That way you can cast the working molds yourself. I have done this 25 years ago with a 3 piece mold.I made about 800-1200 working molds from that rubber mold over 15 years. We sold aroma therapy lamps by the pallet full in the 90's to a large company. I will add I hate the slip business and I farmed most of the work out as I'm not a person who likes the same thing over 50,ooo times. I have 5 lamps left on a shelf. They now cast them all in china and they come apart from the heating and cooling candle heat-thats why they bought from us now they just went back to china during an expansion phase that company is Frontier Herbs which is sold in stores nation wide here in the states.
I know more than I will say.
Anyway that mold is not that hard for master mold person to make.
Sara78 reacted to MatthewV in How Is Made
Uhhhhh start with some basic (whatever you can find) slip casting. As you start to work with the process what is possible and what is difficult will come around. What you are looking at is a combination of experience and meticulous perfectionism.
Most pieces get joined at the leather-hard stage. I see no reason to believe these were done after being fired.
(I suspect the complex ones are made with one mold with several pieces. Never underestimate the amount of effort to hide the signs of how something was done!)
Sara78 reacted to neilestrick in Wedging Clay
I find that most of the clay bodies that we use in my studio are useable right out of the bag without wedging. The key is to cut a cube off of the big block, which can then be made into a ball without folding it up and trapping air bubbles. If you cut a thin slab off the top of the big block, it will need to be wedged. Porcelain always needs to be wedged.
Sara78 reacted to oldlady in Wedging Clay
we discussed this last year and lots of people do lots of different things. learning to wedge is a very important step in your clay education. learn to wedge first and then decide whether to use it as a preliminary step in whatever you will be making. your education in all facets of clay work is what is important now, and wedging is one of the first things to learn. you could not play Mozart's finest piano music without learning the scales.
most of all, have fun.
Sara78 reacted to Bob Coyle in Wedging Clay
Your best friend as a beginner... other than all the friends you will make here... is Google and YouTube. Just go and search on "wedging clay" and you will have access to how all the people of the world approaches wedging. I got 190,000 internet links to wedging and 5390 on line videos on how people do it.
Just Pick the one that works for you. There is no right or wrong way . ceramics has been around for millennia and every aspect is still evolving.
To begin with, just use the clay out of the bag. When you develop scrap that you will want to re-use then you MUST wedge it to get the air out.
Sara78 reacted to Stephen in Wedging Clay
What I've been doing for production for a few years now and not having any issues. We have a de-airing pug mill though so just use the reclaim out of the sleeve as well. I do lightly wedge and cone up and down several times. But like Bob said just go with what's right for you, once you figure THAT out.
Where I have a good routine your's might be different based on all kinds of things including the clay body and the environment everything is used and stored in.
It is confusing and can be maddening when you are starting out. Change something and often your routine will have to be adjusted.
That's why old potters live in the same house for 50 years using the same wheel, kiln, clay and green glaze they started with in 1976 and go into a tizzy when the owner of their supply house dies of old age, retires or worse yet turns it over to their kids who have been waiting in the wings wanting to change everything for years.
Just remember when it comes to pottery, change is bad!