Testing Stains in slips and glazes
In last month's article, we explored the many uses for Mason Stains. This month, we're going to get down to the nitty-gritty of how to go about testing those colors to hone in on your target hue.
Protect your lungs! Anytime you are working with dry materials, you should wear a properly rated and well-fitting respirator!
We're going to explore this process mainly through an exercise of testing one stain color in various concentrations in a decorative slip. This will provide a basic understanding of the process, which you can then build upon with other testing methods.
Step 1: Establish Your Base
To begin, we need to identify a base slip formula. There are thousands of formulas out in the world, in books and online, so do some hunting and choose one that has a good amount of community feedback. You will want to find a white or off-white slip that is intended for your firing range. For surface slips, you will need to consider the clay body onto which the slip will be applied. Choose a stoneware slip to apply to a stoneware body, a porcelain slip to apply to a porcelain body, etc. This will help match up the shrinkage rates of the two bodies and help them fit together better, minimizing cracking. Your base recipe should add up to 100, and the colorant (Mason Stain) will be in addition to that. It's a good idea to test a few different slip formulas on your clay body before committing to one and moving forward to the next step. If all else fails, you can save your clay scraps and let them dry out. Pulverize them into a powder to get your dry slip.
Step 2: Choose a Color
It's tempting to go hog-wild and want to test every color at once, but do yourself a favor and just pick one. You can come back and repeat this process again and again. Sticking with one color at a time helps avoid mistakes, especially when you are first starting out.
Step 3: Prepare Test Batches
Decide how many different increments of the Mason Stain you want to test. I'd recommend at least 5 to give yourself a good amount of data and allow for a wider range. For the sake of this exercise, we'll stick to 5. We need to make up 5 separate mini-batches of our chosen base slip. We don't need much for each test, so 100 grams should be plenty. We will be working at a very small scale, so precision is crucial. Make sure you have an accurate gram scale on hand. Measure out your 5 batches of dry slip in 5 separate containers.
Step 4: Add Mason Stain
Now that you have 5 containers of dry slip prepared, it's time to add the colorant. Decide ahead of time what percentages you are testing and mark your containers and your test tiles. For this exercise, we're going to test the following percentages: 2%, 4%, 6%, 8%, and 10%. This is a reasonable range for most Mason Stains, however there are some that require higher percentages. Carefully measure your stain of choice and add them to your base batches. If you have 100 gram batches, this means you would add 2 grams of stain for 2%, 4 grams of stain for 4%, and so on. If you are mixing larger batches, calculate the appropriate grams for each batch. Carefully stir each batch to combine the dry ingredients.
Step 5: Slaking and Mixing
Add just enough hot water to each batch to completely cover the dry materials. Wait a few minutes for the water to make it's way down through the dry powder, stir gently, then add more water if needed to cover the dry ingredients again. It's best to cover your batches and let them slake for at least a few hours, if not overnight. Slaking is a soaking process that gives the water sufficient time to fully saturate the dry materials. Because of the extremely fine particle sizes, this can take several hours. Using hot water rather than cold water will help expedite this process. Once the batches are properly slaked, you can mix them up. I recommend an electric hand mixer or Jiffy Mixer. You may need to add a bit more water to achieve the correct consistency (heavy cream). Blend until smooth, then sieve with a 60 mesh screen to break up any remaining clumps of dry material. Be diligent to not cross-contaminate your test batches. Clean your mixing utensils and sieve thoroughly between each batch.
Step 6: Test Tiles
Hopefully you have planned ahead and already have some test tiles made up. If not, don't sweat it, just roll out a slab of your chosen clay body and cut out some small tiles. Make sure to stamp or scratch the percentages into the tile somewhere so you know what you're looking at when it emerges from the kiln. Apply 1-2 coats of each batch to it's matching (and well-marked) test tile, and let dry. Bisque fire, apply clear glaze to half the tile, and re-fire to maturity.
The process for testing Mason Stains in glaze follows the same procedures as previously discussed. Instead of dry slip batches, you will have dry glaze batches to which you will add your stain. While the initial process may be the same, there is much more room for error when formulating glazes. The chemical interactions in glaze are much more volatile than in slip, so there is a decent possibility you will run into some glaze defects along the road. Working through these issues by adjusting your recipe will take time, but you will be rewarded with a custom glaze that is all your own. Additional reading is highly recommended when pursuing glaze formulation.
John Britt article in Ceramic Arts Daily (photo below from this article)
DigitalFire article on formulating and trouble-shooting
The Limitless Possibilities of Mason Stains
At the end of the day, using mason stains requires a bit of testing, no matter what application you are pursuing (some less than others). Each different stain has its own properties, and some colors are more powerful than others. You may only need 2% (by dry weight) of Sage Gray, but 15% of Titanium Yellow to achieve the same level of saturation for each color. And those are just slip colorant percentages for cone 5/6. If you want to make a Titanium Yellow glaze, your percentages will be different. If you want to make a low-fire slip, again, your percentages will be different. With so many variables in the mix, it is important to take the time to test!
Spring is Here!
With an unusually warm February come and gone, it's time to really start gearing up for spring! The official start of the season is on March 20th, but we're not waiting around to get to work in the studio! After the lull of winter, there are likely to be some chores that need doing to whip your creative space back into workable shape (I know mine is a horrid mess!), so we've made up a little checklist that might be helpful to you!
Spring Studio Cleaning Checklist
Stepping into a dirty, disorganized studio can really put a damper on your creative motivations. Take a day this weekend to do some spring cleaning, and your artist within will thank you for it!
One question we get a lot is "How much clay do I need to make ____?" Alternately, there is also the "How many mugs can I make with a box of clay?" version. It's something everyone asks at some point in their clay explorations, usually more than once! While meandering through the archives of Ceramic Arts Daily, I came across this great diagram by Robin Ouellette and wanted to share!
If that is too small to read, here's a charted version:
This is obviously just a general guide, and you may need to use more or less clay to achieve these forms. Happy potting!
I can't believe it's already November, but here we are. If you plan on making some of your gifts this holiday season, it's time to get in gear! Between making, drying, firing, glazing, and re-firing, there is a pretty substantial lead time on any clay project, so don't procrastinate! Get ahead of the holiday-gift game and start today. We love these little textured dishes because they are easy to make, look great, don't require many tools, and the technique can be adapted to make almost any form!
Using your rolling pin or hand roller, press the clay onto the texture slab with moderate pressure. Make sure to roll in multiple directions, and all the way to the edge of the mold. You can gently lift one side of your clay slab to check and see if the design is imprinted. If it is faint, continue rolling with increased pressure until you get a good impression.
Carefully remove the slab from the mold and lay it flat with the textured side up. Using your paper plate as a template, cut out the shape of your dish using the fettling knife or a similar cutting tool (you can even use a butter knife in a pinch). Turn the paper plate right-side-up and set your round slab into the center. Lift the plate a few inches off the table and let it drop a few times. This will help the clay settle into the form and take the shape of the plate. If the paper plates you have are not very sturdy, you can double- or triple-layer them to help support the clay.
Using your thumb, gently press on the sharp edge of the rim to soften it. Continue this soft pinching motion all around the rim. Don't worry if it isn't perfect, there will be more opportunities to refine later. Let the plate set up for about an hour, or until it becomes soft leather-hard.
When the plate has set up to the soft leather-hard stage, it can support its own weight without the paper plate form. Once your piece is out of the paper form, gently turn it over and set it on a bit of foam to prevent damage to the texture. Keep in mind that this is a dessert-sized plate, and for larger forms like a dinner plate, you will need to add a support underneath once you remove the paper plate form and flip the clay piece over. I find that sponges work well for this.
Roll out a thin coil and tap one side to make it flat. Score the flat side of the coil and the bottom of your plate on the "shoulder", where the flat bottom starts to turn into the rim.
Brush a bit of water, slip, or vinegar onto the score marks and connect the foot to the plate. Using a rib, blend the coil onto the bottom of the plate on both the inside and outside of the foot. Make sure to use one hand to support the underside of the plate opposite where you are pressing the rib, keeping the foam in between to act as a buffer and protect your texture. Once the foot is blended, you can go back with your sponge and refine the foot and rim. Try not to use too much water, as it will soften the clay again and cause distortion to the shape.
Last but not least, once the foot has set up a bit (about 30 minutes), flip your plate over and give the foot a few gentle taps on a flat surface. This will level out the foot so the plate doesn't wobble.
Tada! You just made an awesome appetizer plate/ring dish/catch-all/soap dish/you-name-it! Aunt Rosie will be in raptures!
Bonus tip: Choose a glaze that accentuates texture, like Mayco'sElements Glazes or Foundations Sheer Glazes!
Most of us at some point will have to ship a ceramic piece, whether it be for a gallery, online customer, or Aunt Bernadette's birthday. After spending hours making a beautiful cup, plate, sculpture, etc., the last thing we want is to hear that the precious cargo arrived in shards! Amaco published this great video that covers the basics of packing pots for shipping:
A Few More Tips
Why and How to Make Your Own
Making pots takes time. Decorating them takes even more in some cases. One thing that is always at the forefront of a potter's mind is the moisture state of the piece. If it's too dry, the carving tool will leave ragged edges. If it's too wet, the clay will stick to the tool and smear. Timing that handle attachment or that mishima scraping is a major part of our art that takes practice and patience to perfect. Let's face it, though: we all have busy lives, and sometimes, time constraints don't allow us to wait for just the right moment. Luckily, there is an easy solution that makes a great addition to your studio: a damp box.
A damp box is a humid container in which to store in-progress claywork. You are creating a makeshift version of this every time you put a plastic bag over an incomplete piece. The advantange of a damp box is that you can do this without the hassle of the plastic bag, or the potential surface marring it can cause.
Now, you could pay hundreds (or even thousands) of dollars for a fancy damp cabinet from a manufacturer, but I'm a broke twenty-something who pinches every penny until they beg for mercy. Why pay all that money for something you can achieve with $20 and 30 minutes of your time?
Once you have chosen your box, you will need some plaster. I prefer a medium-density plaster such as Puritan Pottery plaster or #1 Casting plaster (both are available at Armadillo Clay). You will want to weigh out about 10 lbs of plaster for a 30-40 gallon box. Smaller boxes will use less plaster. Assuming you are using one of the two plaster choices I recommended, you will need about 6 1/2 pints of water to make up that 10 lbs of dry plaster. In a clean bucket, measure out your water, then add in the dry plaster and mix for about 5 minutes. Make sure to wear a respirator! Once your plaster is well-mixed, carefully pour it into your box until you have about an inch depth of plaster in the bottom. Too much, and the box will be very heavy. Too little, and your plaster layer will be prone to breaking when you move the box around. Let the plaster set overnight, lid off.
Your damp box is ready to use! Make sure to leave the lid off when it is not in use, to avoid mold growth. If you do get some mold growing, you can spray the plaster slab with a bit of well-diluted bleach. To recharge your damp box, just pour some fresh water onto the plaster slab. I prefer to have a layer between the plaster and my pots, so I cut some old Orton Cone box liners to make a soft sponge layer on top of the plaster. Once you have a damp box, you'll wonder why you didn't make one years ago!
If you've ever tried handbuilding a piece, particularly one with a large flat surface such as a platter or decorative tile, you've most likely encountered issues with warping. You smooth and carve and sand and perfect, and then it comes out of the bisque with that dream-crushing wobble. Don't worry, you're not alone. Most people underestimate the difficulty of handbuilding, particularly flat pieces like tiles and plates. In reality, there are a plethora of nuances to making a successful handbuilt plate. Here are a few tried-and-true tips to help you avoid that heartbreaking warp:
The spiral usually ends up facing up toward the opening of the bag, so when you just slice a layer off the top, you are taking a whole cross-section of that spiral with you. Not good! The clay particles are aligned differently in the center of this slab than they are at the edge. To avoid starting off on the wrong foot, take your clay pug out of the bag and cut your slice off the side of the pug. This will give you a relatively even section of clay with which to begin preparing your slab.
Now that you have a nice piece of clay, stretch and roll out your slab gradually(don't smash it into shape all at once!), flipping and turning it as you go. This will help align the particles on both sides of the slab evenly.
2. Handle With Care
As you work, try to keep in mind how you are handling the soft slab. Anytime you need to move it, ask yourself: "Do I really need to pick up the slab, or could I use another board to flip/adjust it instead?" Use boards as often as possible to sandwich the slab and flip it, rather than picking it up with your hands. This avoids stretching the slab, which can translate into warping as it dries. Sometimes there's no other way but to just pick it up, though, so when you do, make sure to go slow and splay your fingers to give the slab as much support as possible. Once the slab sets into the leather-hard stages, this stretching risk is all but eliminated. Once the piece is finished, dry it with just as much care! Slow and steady wins the race. Fast, uneven drying encourages warping.
3. Don't Stress, Compress!
While this is more of a general rule of handbuilding, it sort-of applies to warping, so I've decided to mention it. Make sure to compress your edges and attachment seams! The edges of the slab get weaker as you work and move the slab around, so it is important to go back and re-compress those edges to ensure sturdy attachments and strong rims. Clay moves as it dries, and without proper compression on your attachments, those joined slabs will want to warp away from each other, creating cracks.
4. Put a Foot On It
A plate with a foot ring is much less likely to warp than one without. The reason for this is the same as basic construction fundamentals: A broad plane is much stronger with an underlying support brace. The foot ring adds this support and helps stabilize the wide flat span of slab.
5. Don't Wait, Weight!
Weights are a very helpful tool for handbuilders. Most common are small sandbags that can be made at home with old socks and a Ziploc sandwich bag. Fill the sandwich bag with a pound or two of sand, double bag if desired, and place inside an old athletic sock. Tie off the end and voila! Instant high-tech handbuilding tool. These sandbag weights are perfect for plates, applying just enough even pressure to discourage warping as the plate dries. As soon as the plate is soft leather-hard, these weights can be applied. Don't overdo it, though. One or two sandbags usually does the trick. I recommend putting a soft liner between the sandbags and your piece, however, as the texture from the sock can sometimes be left behind. I use a thin piece of foam (like the ones that line Orton cone boxes!) to preserve my plates' surface.
For tiles and other flat pieces, sandwich them between sheets of drywall and let them dry slowly, flipping every day or so. Make sure to wait until the pieces are soft leather-hard before sandwiching, to avoid damaging any decoration on the surface. I also use this technique on larger plates and platters, to help keep the rim level as it dries.
At the end of the day, as with anything clay-related, there is no shortcut to experience. Some levels of understanding can only be achieved through trial and error. Don't get discouraged! Keep making, keep learning!
Do you have an upcoming show or event? Email us with a .JPEG postcard image and the basic info about the show, and we can post it right here on our blog!
Ceramics-related events only, please!
E-mails can be sent to melissa[at]armadilloclay.com.
Please note: The events page is a courtesy for local artists, and we cannot guarantee every submission will be posted.