FrogBlog
Peepholes and Venting
Last week, we got an e-mail with a bunch of great questions about peepholes and venting your kiln when using powdered enamels--like EZ Fire enamels--dry on copper. So, we thought that we would give you some insights on venting for all kinds of enamels on glass, and metals too. Hopefully, this Q&A from Gail will help you in the future... it always helps me! Why does my kiln have a Peephole? Large peepholes (viewports), tapered for a wide view without heat loss, were originally designed for manual kilns so you could see when the pyrometric cones bent. With venting as their secondary function, peepholes allow oxygen to be drawn into the kiln’s chamber and serve as an escape passage for metal oxides, smoke, and water vapor. Do I need a Peephole Plug? Peephole plugs are used to stop air from entering the kiln, not to prevent heat loss. But a kiln shouldn't be vacuum sealed, so It is beneficial to have some air entering the kiln at all times, It is not necessary that the plugs fit tightly. What is the best shape for a Peephole Plug? Peephole plugs are typically made of a lightweight ceramic material that can handle thermal stress well. Many plugs are interchangeable with different kilns, and the type of plug that is chosen is typically based on individual preference. The plugs with a tapered shape are designed to fit in just about any hole. Should I leave the Peephole hole open or closed during firing? For plain old glass fusing and slumping, always fire the kiln with the plug in the hole as it helps the kiln reach temperature more easily. If you chose to leave the peephole out during firing to improve the oxygenation inside the kiln, be aware that this may cause a cold spot in the kiln. When firing dry enamels on copper, leave the plug in the hole until you reach the top processing temperature, then remove it for proper oxygenation of colors as you insert your trivets and fork. When you are firing red, orange, or yellow enamels you should remove the plug so that more oxygen circulates in the firing chamber, keeping the colors bright. When firing liquid enamels on glass, leave the kiln vented or plug out until your reach 1000F. Then place the plug back in the hole. SOME (not all) liquid enamels need oxygen to develop to their juiciest potential! If you want the kiln to cool faster, remove the plug. If you are doing a wax burnout, remove the plug. If you are doing a hollow core metal clay project, remove the plug. Are there fumes that come out of the Peephole that I should be careful of? That depends on what brand of enamels... SAFETY FIRST! OLDER ENAMELS MAY CONTAIN LEAD THAT CAN BURN OFF IN THE TORCH OR KILN and will require proper kiln ventilation of the area. Always do your research on enamels before you plan to use them.
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Observing a Kiln During Firing... What's Normal?
A big thank you to our friend Arnold from Paragon Kilns who helped answer these important questions about observing your kiln during firing. Gail also added some nuggets of information to help round out your knowledge! The heating elements hum when they turn on. The sound is generated because the elements vibrate in the brick grooves due to magnetism between the coils. So, it's totally normal! The sound actually diminishes as the kiln gets hotter because the elements soften. Notes from Gail: This is also true in kilns with suspended quartz wrapped tubes, but it's harder to hear since the elements are inside the tubes. Elements that are wrapped around ceramic rods probably won't hum much at all. The clicking noise of an infinite switch-operated kiln is also normal. It is the sound of an infinite control switch cycling on and off. When the clicking turns into a popping noise, the switch is probably about to fail. Notes from Gail: This isn't happening if you only have a digital controller. But, some kilns have an infinite switch in the lid with a digital control of the body. You'll be hearing the clicking on those. Digital Relays are another source of clicking. To turn on the elements, a digital controller sends twelve volts to the relays. The relays, in turn, act as switches and send full voltage to the elements. The relays click every time they turn on. A chattering noise, however, indicates that a relay is about to fail. Notes from Gail: This is why I'm a big fan of MDRs (mercury displacement relays) and SSRs (solid state relays.) They are much quieter and worth the money to upgrade in the long run! A crackling noise followed by a loud POP from the kiln's switch box usually means that a loose electrical connection has just failed. If you hear crackling, which sounds like sparks, turn off the kiln. The loose connection creates a tiny electrical arc, which overheats and burns electrical parts. Rapid arcing causes the popping noise. Whenever you change elements or have the switch box open for any reason, check all of the wire connections. Make sure they are tight... The power must be disconnected, of course. Tug on the wires. If a wire pulls out of a terminal, replace the terminal with a new one using a good crimping tool. Remove any dust before closing the switch box. When you replace elements, make sure the connections are tight. Notes from Gail: This happens in clamshell kiln lids occasionally, since the lid is constantly being opened and closed, the element connections an get loose. Don't despair, it's an easy repair. Why is there a gap between the kiln and the lid near the hinge? The gap under the lid of a cold kiln at the hinge is normal. As the kiln heats up, the firebricks expand, which causes the body of the kiln to grow taller and close the gap. The gap is designed to help prevent the front of the lid from rising at high temperatures. Notes from Gail: Yup! The lid on my kiln is rising at the front during firing. What is the cause? During firing, the wall bricks expand. This pushes the lid upward. If the hinge does not have sufficient play, the lid will rise at the front. If this happens, please do not put a weight on the lid to hold it down. That will only damage the lid. Instead, check for binding in the hinge. Notes from Gail: If this is happening, call the kiln manufacturer and ask them how to mitigate the problem. They'll walk you through an easy fix for your type of kiln. If this becomes extreme, it can crack your kiln lid so, it's important to take care of this issue sooner rather than risk a messy, crumbling lid. My front-loading kiln has a gap between the door and the firing chamber. Is that normal? There should be no gap between the door and the firing chamber at the side toward the door latch. There should be a gap, however, at the hinge side of the door. When the kiln is cold, you should see a gap of about 1/16 between the hinge side of the door and the firing chamber. As the kiln heats, the firebricks expand. Without a gap, the door will bind at the hinge and cause a gap at the side toward the latch. Notes from Gail: Some kilns have gaskets that fill the space and seal the door opening. If you have a gasket that is worn, it's easy to get a replacement from the manufacturer and should help alleviate the issue. New doors can also be purchased if needed. I am concerned about the light that appears under my kiln lid during firing. The light that you see under the lid is normal as long as the lid is not rising in front. The inner lid surface expands more than the outer cooler surface. Therefore, it bows inward slightly toward the firing chamber. This is normal. For this reason, you will see a thin line of light around the lid since the lid is no longer a flat surface resting on the flat firing chamber sidewalls. Surprisingly, there is very little heat loss from around the edge of the lid. Notes from Gail: If you suspect this is causing a cold spot during firing, call your manufacturer. If this becomes a serious issue, you can purchase replacement lids at reasonable prices for most top loaders.
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The Firing Stages of Glass
We get lots of questions about the overall firing process... fast or slow, open or don't open? We also understand the anxiety that accompanies firing your kiln for the first time or, trying a new technique. Don't forget, we are glass-a-holics just like you... and, have had a few missteps along the way. With that said, here is a quick look at the stages of firing. So, the next time you have a question... hopefully, you will have the answer! Initial Heating from Room Temperature (room temperature to 1200°F range) During the initial heating, the glass is very brittle and susceptible to breaking if it’s heated up too quickly. Imagine a large notebook laying flat on a kiln shelf, it has a top and bottom surface and four sides. The book also has interior pages... basically, anywhere between the exposed surfaces. If we heat the book... or glass too quickly, the surface area will expand faster than the interior of the glass. This is what creates tension within the glass and, breakage... a.k.a. thermal shock! So, during this stage, it’s best to take a super conservative approach and slowly heat up the glass. Choosing between torch enameling and kiln enameling depends on project size, heat control, repeatability, and the equipment already available in the studio. At the end of this temperature range, somewhere between 1150°F to 1200°F, it’s a good idea to add a heat soaking period to allow the project to equalize to the same temperature throughout. Never peek in the kiln during this stage, or you increase the risk of your thermal shock breakage.Process Heating (1200°F to 1500°F range) The glass becomes softer and more fluid. During the process heating stage, the glass can be fired more quickly to the target temperature and soaked only long enough to achieve the desired look. It’s important not to hold the project at these temperatures for a long period of time, or you run the risk of devitrification (a visible clouding of the glass surface due to crystallization). Fast Cooling (1500°F to 1100°F range) After the finished look has been achieved, it’s important to cool the inside of the kiln and the glass as quickly as possible to stop the firing action so that it “freezes”. During the fast cooling stage, the surface of the glass is cooler and it has contracted more than the heated center which remains expanded, thus introducing stress into the glass piece. Annealing (1100°F to 700°F range)At the beginning of the annealing stage, it’s necessary to heat soak the glass for an extended period of time to allow the glass to equalize in temperature throughout and release the stress that’s in the glass. This makes the glass more stable. Then the glass is slowly cooled through the annealing temperature range to better ensure the glass piece is free of internal stresses and is physically stronger. NEVER OPEN THE KILN DURING THIS STAGE! I repeat... NEVER OPEN THE KILN DURING THIS STAGE! Cooling to Room Temperature (700°F to room temperature range) After the glass temperature has cooled below the annealing temperature zone, the kiln can be turned off to allow it to cool at its own pace to around 150°F – 200°F. Again, to avoid thermal shock, do not open the kiln until it has cooled down to at least 200°F. Even at this temperature, the glass is very hot, so do not attempt to pick it up in your bare hands. It may look cool but, it's hot! Simply open up the lid of your kiln and allow the glass and the kiln shelf to cool down to room temperature.Together they comprise a single firing cycle (room temp to room temp).The Bullseye Glass TechNotes 4 is also a very helpful resource for the explanation of Heat & Glass, as understanding the behavior of glass within these different temperature ranges will ultimately be the key to your success!
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When the Kiln Lid Flakes...
Great information about kiln lid repairs from our friends at Paragon... At Paragon, they coat the inner lid surface of all kilns to reduce brick dust. Sometimes the refractory coating is too thick so, it will blister and flake off when the kiln is fired. An especially thick coating looks like a network of peeling cracks similar to a dried mud puddle. This cracking is due to the difference in expansion between the firebricks and the coating. Conversely, correctly applied kiln coating will look like it disappeared after the kiln has been fired. The good news is that cracked lid coating is easy to repair. Just lightly remove the blistering coating with sandpaper and apply a new coat of liquid kiln repair cement. Keep in mind that the natural tendency is to apply too much lid coating because it just looks better than a thin layer. If done correctly, you should still be able to see the firebrick pores under the coating! First, shake the container very well! Then, pour some of the coating into a bowl. Make sure to stir it just before you apply it to the firebricks. Apply the coating with a large, soft sponge. Moisten the sponge with water; then squeeze out the excess... this is a very important step! Dip the sponge into the bowl of kiln coating. Wipe the coating over the lid surface. Do not let excess coating run into the element grooves of the kiln. Applying a light coat will prevent this from happening. If the coating drips along the edges of the grooves, remove by wiping a cotton swab or rag along the groove. Many people have asked us... "What is the difference between kiln cement and Liquid Kiln Coating? Can a lid be coated with a thin mixture of kiln cement?" The answer is YES! Kiln cement thinned with water will work as a lid coating. Liquid Kiln Coating is simply a mixture of kiln cement, fine brick dust, a gumming agent, and water. The great news is that lid coating lasts for several years. So, it's not something you need to worry about on a daily basis. But, if you start getting kiln brick dust on your work, maybe it's time to re-apply. Some kilns such as the Paragon CS-14S allow you to upgrade to a fiber top, which helps to keep your kiln cleaner and reduces the chance of debris in your pieces.
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Get the Look with Stripes and Dots
Bullseye Glass Quick Tip: This Quick Tip, shows you how to get a fun summer look using rods to easily create simple stripes and dots. Stripes - Use a complete layer of rods as the base, then cap with 3 mm Clear and fire to a full fuse. To ease set-up and prevent rods from rolling, make yourself a square frame from 1/16" fiber paper. After firing, the shelf side will have a smooth, semi-matte finish, while the top has glossy goodness. Slump with either side up! For variation in line width, place a stringer in the low spot between rods. Stringers are great and will stay perfectly straight through the fuse. If you are looking to cut rods in bulk, try securing the bundle with rubber bands and using a wet tile saw. Not only will this save time, it will also make your rod cuts straight and even! Dots - Nip rods into 3-5 mm sections, and arrange them on a sheet of 3 mm Clear. Place this on a base of 3 mm opalescent and fire to a full fuse. To maintain a square footprint and control volume, use shorter snippets closest to the perimeter. Designer Marc Jacobs says... "There is never a wrong time for a polka dot" and, we totally agree!
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Easily Identify the Coated Side of Dichroic Glass!
This is one of those questions that can make you crazy... How do I know which side of the dichroic glass is coated? Originally created for the Aerospace industry, dichroic glass is a created by adding a multi-layer coating to one side of the glass using a highly technical vacuum deposition process. Dichroic glass is available with a transparent or opaque glass base. On a transparent base, some light dichroic colors look the same on both sides of the glass which made finding the coated side all but impossible... until now! First, place the dichroic glass over a dark background. Then adjust your viewing angle until the surface reflection overpowers the dark background. Next, lightly touch the glass surface with a paper clip and you will see the paper clip reflected in the dichroic coating. Here is the most important step... Does the reflection meet the paper clip, or is there a gap between the paper clip and its reflection? On the coated side of the glass, the paper clip will touch its reflection. On the base side of the glass, a gap will separate the paper clip from its reflection. And, the gap will actually equal the thickness of the glass! So, why is it important to know which side of the dichroic glass is coated? Cutting - Always cut on the non-coated side of the glass. This helps to prevent chipping, especially on the heavily textured glass. Coated Side Down - When using the coated side down or capped with clear glass, the dichroic glass will have a smooth glossy surface and sparkle like glitter! It will also change colors between the transmitted color and a completely different reflective color, depending on the angle of view. Coated Side Up - Conversely, if you create with the coated side up or uncapped, the dichroic surface will have a highly metallic sheen. The piece may additionally be rough and textured depending on the type of dichroic glass you are using. In the end, there is no wrong way to use dichroic glass... capped or uncapped, it's all a matter of choice. Actually, in my favorite workshop, we didn't fuse it at all! It's all about the experience... the more you know, the greater the range of effects you can achieve! As a glass artist you need to check out Bullseye's great selection of glass supplies on Kiln Frog. It also can't hurt check out our selection of grinders from Covington and Ameribrade.
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Dual Media Kilns - The BEST of BOTH Worlds!
One of the main reasons we love Dual Media or DM kilns as they are the ultimate in flexibility! Let's face it... sometimes you just need options!Dual Media kilns are kilns specifically designed for firing ceramics AND glass. If you have ever wondered about the differences between a glass kiln vs ceramic kiln, the core distinction is in how they heat: glass kilns fire from the top, while ceramic kilns fire from the sides. Technically speaking, ceramics and glass can be fired in any kiln that achieves the temperature you need. Jen-Ken Ceram-a-Glass 2422 The Ceram-a-Glass series from Jen-Ken Kilns is a great example of a dual media kiln. They are top and side firing for glass and side firing only for casting, and ceramics. Switching from one mode to the other is super easy as all Ceram-a-Glass kilns come equipped with a side toggle switch. Simply toggle up for the glass fusing mode up which allows you to fire up to 1700°F or, toggle down for the ceramics/casting mode for up to 2100°F. Some of the Ceram-a-Glass kilns even have 3" brick so you can go as high as 2300°F! Paragon Janus27 The Paragon Kilns Janus series was specifically designed to fire both pottery and glass. According to Paragon, the Janus name was derived from Janus, the Roman god, who is often depicted as having two faces which faced in opposite direction. In the Janus kilns, you can easily select between glass and pottery with the flip of a switch. With the switch in the glass position, heat comes from the top elements and the middle sidewall element. With the switch in the pottery position, heat comes from only the sidewall elements. Olympic Kilns also offers a complete line of Dual Media kilns, plus you can easily add a lid element to any of the HE models! An ON/OFF switch activates the lid element when fusing is desired. Olympic 1818HE The Olympic Dual Media kilns are stackable (meaning they are constructed of stacked rings) electric kilns that are designed to come apart so that you can easily move them from one location to another, easily work on one section of the kiln without taking the entire electrical system off the kiln, and increase or decrease the depth of kiln as needed.So, what else do you need to know if you plan to purchase a Dual Media kiln?HEAT RISES... When you are using a Dual Media kiln in ceramic mode, only the side elements are firing, BUT since heat rises you are "cooking" the "sleeping" lid element. This high-temperature baking of a "sleeping" element will shorten its lifespan. This is not really a big issue as long as you are aware that you may have to change out the lid coil more often than the body coils. It's just the nature of the beast!USE OF AMPERAGE... A Dual Media kiln will use more power in the ceramic mode than in the glass mode. As you know, clay needs to be fired at higher temperatures than glass, so it's just physics that you'll be using more power. It's not a tremendous amount more but, something to keep in mind when you are looking at your electric bill.STACKING vs NO STACKING... Dual Media kilns can hold a lot of stacked shelves when firing clay pieces. BUT, just because it can do that in ceramic mode, doesn't mean you can do that in glass mode. The rule for glass is still... one shelf 6-10" from the top element! This means you'll really need to elevate your kiln shelf to get it high enough to get an even firing. Also, if you keep shelves in your kiln below the one that you are using to fire the glass, the kiln will take longer to heat and cool due to the abundance of refractory material (clay shelving) inside the kiln. Knowing this ahead of time will save you headaches and frustration.We like to think of a dual media kiln as the gift that never stops giving! It allows you to explore your artistry without having to purchase an additional kiln. In the end, only you know how much clay vs. glass or casting work you plan to do, so... if you like to keep your creative options open, a Dual Media kiln may just be the right choice for you!
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