FrogBlog
Kilns vs. Ovens vs. Furnaces | What's the Difference
When choosing a heating method for hardening, curing, or transforming your projects, kilns, ovens, and furnaces are all important options. So, what’s the difference between these three terms and how different are they?
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Meet our new Gas Fired Kilns!
Introducing the newest additions to the family, Olympic's Raku and Torchbearer Gas Fired Kilns. If you’re looking for a way to add a completely different dimension to your ceramic art then you’ll want to investigate propane and natural gas kiln firing. What are Gas Fired Kilns? Well, Gas Fired Kilns are heated by the combustion of propane or natural gas. With gas firing, you can control the internal firing atmosphere of the work environment, which directly affects the outcome of your glazes and clay bodies. Gas kilns have the advantage of firing to very high temps, often exceeding electric kiln temperatures of 2350°F. In comparison to wood fired or non-electric methods, another advantage of gas kilns is that they do not require stoking to maintain their temperature. Reduction Firing Having both the ability to control the temperature and firing atmosphere of your work environment is the chief motivating factor for most artists in choosing a gas kiln. Creating an atmosphere of deprived/starved oxygen where carbon monoxide is produced which is known as reduction. The reduction cycle is responsible for a wonderful and unique palette of colors that occur when oxygen-deprived molecules seek the chemically bound oxygen from minerals that are in clay and glazes. Various glaze colors can be achieved in a reduction firing. The Copper reds are very hard to achieve with other firing methods, but in reduction a wide range of reds can be achieved, and these are some of the most dramatic. Rarely can a reduction atmosphere be achieved in an electric kiln safely. Gas Fired Raku Kilns Olympic Raku gas kilns are specially designed for raku work by retaining heat in the firing chamber when elevated by the turn of a hand winch, allowing easy access, while trapping the heat in the kiln and away from the operator. Today potters can create the ancient Japanese technique, raku and its unique beauty, metallic luster, and colors with an Olympic Raku kiln. The raku firing process involves reducing (starving the oxygen) the glazed raku pottery in combustible materials such as leaves, sawdust, newspaper, etc. When the pieces are ready to take out of the kiln, they are placed in galvanized trash containers with combustible materials and covered. Once the pieces are cooled down, they are removed from the containers, washed, and reveal the rich warm effects of raku. (Sounds fun, doesn't it?) Gas Fired Torchbearer Kilns Torchbearer kilns, with their portability, offer many advantages such as low initial cost, convenient movement for demonstration firings, and for use in situations where space does not permit the installation of large permanent kilns. Torchbearer models fire using either natural gas or propane and may be easily adjusted for oxidation and reduction firings. The multiple burner configuration gives the Torchbearer even heating characteristics, fast controllable firing times, and economical operation. How do you operate an UpDraft Gas Kiln? Once the kiln is hooked to a gas source, each burner may be ignited with a fire stick and the primary air-adjusted for each of the air mixers or burners. Before attempting to adjust burners, loosen the locking screw. The locking screw is not re-tightened unless the kiln is moved. Air adjustment is accomplished by revolving the adjustment shutter plate up or down below the air mixer. The recommended starting point for natural gas is 1/4” and for propane 3/8” – 1/2”. The air adjusting plate is locked between the burner orifice and the burner. To move this plate the burner must be loosened slightly from the brass orifice which threads into the center of the burner. Air adjustment is very important and should be accomplished with care. After loosening the locking screw and the burner from the orifice, rotate each plate to ensure it will move freely. Next position each air adjustment plate so the air inlets are 50% open. The kiln may be ignited while fine air adjustments are being made. A properly adjusted kiln will have all flames uniform in appearance with the transition from the candle flame to intense flame occurring at the same time for each burner as the gas valve is opened. The kiln operates most efficiently when the intense flame has a bright blue color. Propane gas will not generate as intense blue color flame as natural gas. If the flame tends to blow out when the gas valve is opened the air inlet should be closed slightly. The air adjustment of the burners is not be changed once the optimum settings are obtained; however, reduction firing in the kiln may be accomplished by closing the air inlets. The easiest and most reproducible reduction is obtained by placing a damper (kiln brick, kiln shelf ) over the vent hole in the lid. If you plan to use natural gas with your kiln, a large burner is necessary when used on natural gas pressure, you will need 6-8 inches of the water column. If you order your kiln for household natural gas use, it will be equipped this way. The natural gas pipeline that connects to the kiln needs to have a 3/4" inside diameter. If you plan to use propane gas, your tank must have a low-pressure regulator like those on a camper trailer. If an adjustable regulator is being used, about 1/2 pound pressure is necessary. The gas pipeline needs to be a hard line with a ¾” inside diameter. The line should run 20 – 40 ft. long from the propane tank. The larger the tank the better; however, a five (5) gallon tank is the minimum size for the 1827G or 18 Raku, and a 15-gallon tank is the minimum size for the 2327G/23 Raku and 2827G/28 Raku kilns. Due to gas flow, the propane tank may tend to freeze solid. If ice is observed forming on the outside of the tank, water can be run over it to help keep it melted. The tank can also be lowered into a large bucket of warm water. When portable tanks are used for rakuing, keep gas tanks at a safe distance from the kiln. Gas Kilns Options - We think this safety add-on is a must! The ignition system is used to: Light the multiple burner system from one point Maintain the flame on each burner Re-ignite any burner that may extinguish The thermocouple safety shut-off will stop the gas flow if the flame is lost entirely. Learn more about how to operate the ignition system and its thermocouple here. High Limit Controller - Make it Digital! The High Limit Controller provides a digital reading of the temperature during the firing and shuts the kiln off at a preset temperature. The controller is wall-mounted and requires a 120-volt outlet. The controller may be retrofitted after the purchase of an Olympic Torchbearer or Raku gas kiln. Gas Kilns offer many more options to customize and make your own! Check out our selection of Gas Fired Kilns here. To get more info on Gas Fired Kilns, visit our Gas Kilns 101 page to learn more. There is so much more information on gas kilns on our site. So, if you want to go on the deep dive it's worth the trip! Enter a new ceramic art dimension with these Olympic Gas Fired Kilns. We are so excited to see the results of your work! *See our shipping pages for shipping information specifics.
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Bullseye Glass Index of Frequently Asked Questions
Do you have exploring questions about Bullseye Glass and how to use it? Their Index of Frequently Asked Questions can be a helpful guide! It contains anything and everything you ever wanted to know about Bullseye Glass. So, get comfortable... this is a TON of great information! GENERAL Is Bullseye glass COE 90? Can I use a ceramic kiln for glass? How can I learn to cut glass? Is Bullseye glass compatible in all conditions? Is Bullseye glass food safe? What are "striking" glass colors? What should I know about studio safety? What's the specific gravity of Bullseye? How do I know which clear Bullseye glass to use? Is there bubble-free glass? Why should I choose Bullseye glass over other glasses? New to using Bullseye Glass? COLDWORKING What is coldworking? Besides sandblasting, how can I remove devit? Can I sandblast glass to remove devit? How do I coldwork my kilncast piece? How do I get rid of sharp edges on my project? KILNFORMING What is kilnforming? How and why should I clean glass before firing it? How do I prevent glass from sticking to kiln shelves? How do I restrain glass flow? What is annealing? Why is it necessary? What is devitrification or devit? What is firepolishing? What is fusing? What is slumping? What is tack-fusing? What schedule should I use for annealing? Why should I fuse and slump glass in separate firings? Want to see the full list? Check it out here... Index of Frequently Asked Questions!
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Everyone Needs a Good First Aid Kit!
A good first aid kit is a must in all studios and workshops, as accidents can happen anytime, anywhere, and it’s better to be prepared than to find yourself scrambling around for a bandage or disinfectant. Been there, done that! Let's face it... we all know it's gonna happen! A small cut may seem insignificant at the time, but if it gets infected you could be out of action for weeks. This is especially important in a teaching environment so, if you have students, make sure you are prepared! An effective first aid kit provides plasters, bandages, scissors, tweezers, and antiseptic wipes, as well as burn ointment, eye wash, and gauze pads. Here are links to our favorite First Aid Kit essentials: Johnson & Johnson Red Cross All Purpose First Aid Kit Clean, treat, protect, and care for cuts, scrapes, minor burns, itches, pain, skin rashes and insect bites with the Johnson & Johnson Red Cross All Purpose First Aid Kit. This versatile kit contains 140 first aid essentials, including cleansing wipes, gauze pads, antibiotic ointment, itch stopping cream, acetaminophen caplets, an instant cold pack, bandages, non-stick pads, rolled gauze, and more. Supplies come packaged in a durable, plastic box that keeps your items accessible, and organized! Medipoint Splinter Out Splinter Remover If you have anything in your studio or workshop, this is a MUST! Maybe, we should have made it #1... as everyone who works in glass knows that those splinters are the worst! Splinter Out is better than a needle because it is steam autoclave sterilized, and has a sharp tri-bevel point that is designed for loosening and pulling out splinters. There are 20 sterile splinter removers per box. Wall Mountable Eye and Skin Flush Station Eyewash Stations are critical! They are intended to mitigate eye injuries when control methods (eyeglasses or protective eyewear) do not prevent exposure to a physical or chemical irritant or biological agent. This Eye and Skin Flush Station includes two bottles of eye isotonic buffered solution with wall mount. Plus, an eyecup for easily focusing the fluid stream into affected eyes. Natural Burn Ointment / Silver Sulfadiazine Cream When you accidentally touch the bead or piece of metal because it looks cool... it becomes pretty important to have a good burn cream close by! FYI... This was actually the first thing I ever used from our first aid kit! ASAP365 Silver Gel by American Biotech Labs is formulated using their unique and patented 20 PPM SilverSol Technology solution. This silver gel can not only help to hydrate your skin but has also been shown to promote natural healing so, it's perfect to use as a natural burn ointment. WARNING: If you have a sulfur allergy, this is NOT for you! Keep in mind that a first aid kit is meant to be used to treat minor cuts, abrasions, and burns. You should never rely on a first aid kit to handle more severe injuries. As an Amazon Associate, Kiln Frog may earn from qualifying purchases.
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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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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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