Microwave Kiln * Microwave Kiln * Microwave Kiln * Microwave Kiln * Microwave Kiln

MICROWAVE KILNS (MICROKILN)

Microwave kilns are really popular now! You'll see these instructions all over the internet (in some cases, verbatim!) and in other companies' printed materials and books! One seller even copied a picture of a pendant that I made (below) to advertise his microwave kiln and used the picture next to one of my advertisements!  The rage is on!

I have found a way to offer First Class Mail International INSURED mail. This method is about $10 cheaper than USPS Priority Mail International. It might take a few days longer to reach you but the savings are worth it!

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General Information

Microwave oven kilns -MicroKilns - allow you to fuse glass jewelry, process silver metal clay or fire ceramics in an ordinary microwave oven. I have directed you to this page to help you learn more about a  MicroKiln OR because you have already purchased one and need to know how to use it. If you appreciate the many hours I spent researching this material and posting it on this website, please purchase your MicroKiln from me.

Welcome to my website, www.microwavekiln.com.  Click here to purchase a Microkiln. I also sell Microkilns on various other e-commerce sites.

The pendant shown below was made of Bullseye fusible glass and dichroic glass; it was fully fused in five minutes. The bail was affixed after firing. The second picture is a size comparison between small and medium Microkilns (the pendants measure one square inch). PLEASE NOTE: A popular new brand of microwave kiln does not state a size but it is SMALL. Check the measurements!

INTRODUCTION & SAFETY

IT IS IMPORTANT THAT YOU READ ALL OF THIS MATERIAL BEFORE USING YOUR MICROWAVE KILN! Please do not lend your microwave kiln to a relative or friend unless they have read every word here, too!

Click here for official Microkiln Operating Instructions. Please print and read before using your MicroKiln. These instructions highlight glass and ceramics.

Art Clay Silver is associated with microwave kilns. Here is their manual. Read it carefully as this information is their official "word" on the subject of safety requirements and it addresses how to use Art Clay Silver. (Art Clay Silver is available here). Please read this before using your microwave kiln! And please note #3 where it says, "Heating time would take longer if the wattage of the microwave is less than 500 watts...." This also means that if your microwave's wattage is MORE than 500 watts that your beginning firing times should be less than the times shown.  And another caution is to allow your microwave oven to cool at least 20 minutes between firings.

Mr. Jack Ludwig of American Beauty Mirrors in Chicago, Illinois, sent a very detailed instruction booklet which accompanied a Micro-Kiln that he purchased 15 years ago. Access this archived, "official," very comprehensive and useful treasure here. Thank you, Jack!  This important caution is included in that material, "Always clean the inside of your microwave oven after using MicroKiln and before using your microwave oven for food preparation." A separate, dedicated microwave oven is recommended. This material includes information about firing GLASS and CERAMICS.

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The following information has been compiled from various sources and contains my comments.

The microwave kiln is safe to use in any microwave oven but firing times will vary depending on wattage. Do not fire longer than recommended firing times. Allow 20 to 30 minutes between firings to allow the microwave oven to cool. The small microwave that I have uses 950 watts and it generally takes 5 minutes to fully fuse a pendant, but it may take only 4 minutes or less in a 1200 watt microwave oven.  Overfiring lessens the life of a microwave kiln.  A MEDIUM MODEL WILL TAKE LONGER TO FUSE GLASS. Let your project cool 20 minutes and then refire for any additional needed time. If nothing happened, you did not fire long enough!

Do not fire for 8 minutes, then add 2 more, then 1 more. Instead, remove kiln and let it cool down after each firing. Then you can add more time. The microwave oven needs to cool down inside from the heat the kiln generates. Overheating your microwave oven can cause it to blow a fuse.

This kiln can be used in conjunction with a traditional kiln for pre-fusing small pieces of glass, firing precious metal clays, or in the area of ceramics, or it can be used as your sole kiln for firing small pieces. Regardless which way it is used, there are real savings in time and electricity! And microwave kilns are FUN!

Did you know that Vicki Payne once did a video about fusing glass jewelry in a microwave kiln?

Microwave kilns are sold by craft retailers throughout Europe and Australia and I usually see them advertised in conjunction with Art Clay Silver. But when I searched American sources, I found ACS usually was associated with Paragon Kilns. I did searches and found that Paragon makes a Quick Fire 6 kiln from ceramic fiber - as microwave kilns are. 

A PMC Hot Pot also has a ceramic fiber shell.

MicroKiln, Paragon Quick Fire 6, and PMC Hot Pot Kiln

Did you notice the microwave kilns described in Mr. Ludwig's archived contribution were guaranteed against defects in material and workmanship for 3 years from the date of sale?

Because the materials are similar, I am posting Paragon Quick Fire 6's safety instructions here. Not all of these tips would apply to a microwave kiln, but some might. I cannot over-emphasize that it is very important for you to be mindful of safety when using a microwave kiln!

In a popular internet forum someone expressed fear that heat will "geyser" out of the hole in the top and the microwave oven will catch on fire. In order to avoid even the slightest possibility of this happening, you should immediately take the microwave kiln out of the microwave oven after firing, place it on a heat resistant surface and away from flammable materials. Do not place it under upper kitchen cabinets, etc.  My supplier said if the microwave kiln were left in the microwave to cool repeatedly, eventually this excess heat coming out of the hole in the top would make the plastic ceiling of the microwave quite brittle and it would probably start to crack. He said that he has personally done hundreds of firings over a short period (3 days) while demonstrating the microwave kilns at trade shows and while the microwave oven did get quite hot from all the firings there was no damage to it or the table it was sitting on.

In the user's manual that Mr. Jack Ludwig contributed, it is stated,   "It is important that there is at least 2 inches between the top of the microwave kiln and the ceiling of the inside of your microwave oven."

Very, very rarely a small  flame might appear at the top hole where there was no other possible source of flames except the shelf paper.  The flame might extend 1/2" out of the hole while it is firing in the microwave oven. We do not consider this a fire hazard as long as there is sufficient clearance to the inside roof of the microwave.  In order to prevent this from happening, cut shelf paper size to match your project so that there will be enough coverage but not excess. Paper which is cut to size and covered would have less chance of igniting. AGAIN, DO NOT LEAVE THE MICROKILN UNATTENDED WHILE FIRING!

My supplier has said if you were to put a microwave kiln that had just finished firing underneath a flammable surface with less than a couple of inches of clearance you might be able to set it on fire depending a great deal on the specific conditions. You should not put a hot microwave kiln in proximity to any surface that is flammable or that could melt. Melting a kitchen counter by putting a hot microwave kiln directly on it (which we also warn against doing) is a much more likely problem than starting a fire from the flue hole gases. Also we have had the flue hole gases tested when using our Multipens on glass or ceramic and they are non-toxic and quite safe for use in a microwave also used for food.

Based upon the material contributed by Jack Ludwig, the word "graphite" should be used where Deborah used the word "granite."

In addition to the microwave kiln, you will need to purchase a microwave oven, glass, Bullseye Thin-Fire shelf paper or fiber paper. These supplies are available at any stained glass or ceramics retail store. Some are also available at www.microwavekiln.com. You may use kiln wash but allow it to dry thoroughly before using your Microkiln. We now recommend a combination of kiln wash and shelf paper as the best coverage, but this is a recommendation only. I do not use kiln wash. If you wish to use kiln wash, apply several thin coats on the base, allow to dry thoroughly. Re-apply kiln wash every 3-5 firings or as needed.

You need a pair of  inexpensive gloves (garden gloves are fine) which will be used every time you move the microwave kiln from the microwave oven or remove the top. I like knit ones best because they are a bit thicker. 

And you will need a heat-resistant surface such as heat resistant brick, kiln shelf  or fiber brick on which to set your kiln after removing it from the microwave. Otherwise a hot kiln could cause a fire or burn to the surface.

Contrary to a recent author's recommendation, using three ceramic posts to keep a microwave kiln up off of the glass tray when firing is not necessary. The glass tray will not break. Read the first three "official" manufacturers/distributors' linked documents on this page and you will not find any such recommendation (One of those companies is Art Clay Silver). This same author contradicts herself when she states that "the outside does not get very hot on quick firings" so how could it possibly break a pyrex glass tray? Also, kiln wash is optional, not required.

It is not a toy and is not to be used by children. IT IS A KILN! Please do not allow small children in the same room when you are firing! Use at your own risk and follow all recommended and common-sense safety precautions! Sellers are not responsible for accidents or injuries caused by hot kilns and your using one purchased from this seller acknowledges that you use it at your own risk! And please don't let your cat rub against it!

Before using your microwave kiln, think about "what if" I dropped my hot microwave kiln, what would I need to have immediately available to pick my hot project up with? A pair of metal tongs? Then always have metal tongs readily available while you fire. A metal dust pan and a metal implement such as an egg turner would serve the same purpose. A ceramic tile floor and a carpeted floor would require very different remedies. Think of other scenarios which are based upon the area where you will be working.  And keep a box of baking soda handy, too!

One seller recommends putting a ceramic fiber blanket on the floor of the microwave oven if the it does not have a turntable.  As the outside of the microwave kiln does not get dangerously hot this is optional as long as you remove the microwave kiln from the oven immediately after firing has finished.

Another seller recommends removing the spinner from the microwave oven before firing. When one of my customers asked why, the answer was to prevent the project from moving around. So that recommendation is not a safety issue. That seller also recommends using ONLY a microwave oven with a metal interior and it must be 1200 watts.  As microwave ovens fitting either one of those two criteria just recently started being manufactured, that recommendation is optional. (Microwave kilns have been in use 19+ years). I personally recommend that a spinner be used to ensure even heating as I have personally seen unrepairable damage done to a microwave kiln where hot spots were the only possible cause of damage. (It is a rare occurrence, but it does happen).

Do not put any material in the microwave kiln that has not been recommended. Among those things that are not recommended are high temperature wire and iridized stained glass (based on my personal experiences), and gold PMC (precious metal clay). 

Please remember that a traditional kiln is composed of fireproof materials and a microwave oven is made of materials that can burn under certain conditions SO don't try to burn off wax or cork clay or wood clay or any other flammable material in a microwave oven kiln! And don't use nail polish to glue your glass together!!!!!! (A lady actually told me she did this!) WAX WILL SET YOUR HOUSE ON FIRE.

Also, protect your Bullseye Thin-Fire Shelf Paper from drifting aerosol can contents such as silicone, spray glue, cooking oil, insect repellents or killers, etc. Do not allow shelf paper to become contaminated with flammable residues.

Before you use your kiln for an actual project, you should place the empty microwave kiln into the microwave oven and fire for three minutes. Let cool for about 20 minutes and you're ready to do your first project.

Microwave kilns are suitable for one-of-a-kind projects. For unknown reasons, it is fairly difficult to obtain identical matched-pair results from project to project.

OK! Let's have some FUN!

Check out my dichroic glass and fusible glass supplies here!

Firing times will vary depending on the wattage of your microwave oven.

You can satisfactorily use stained glass scraps to create jewelry as long as you use only one color OR two or more glasses that have the same coefficient (this requires testing for compatibility). Based upon my personal testing experiences, do not use iridized stained glass! Fusible glass is recommended. There are two major classes of fusible glasses: COE 90 and COE 96. Do not fuse them together! They are not compatible! Your jewelry will crack if you do.

Do not attempt to fire glass trinkets or objects that you did not originally make. There is no way you can know what materials went into that object (painted surface, glued surface, acrylic on the surface,  etc.) and firing an unknown material could be very dangerous!

Cut your glass and clean it. Use a dry (non-oiling) glass cutter for cutting glass which will go into a microwave kiln. Traces of oil will catch on fire! Alcohol is great for cleaning, but be sure to dry thoroughly before putting into the microwave. In order to prevent leaving fingerprints on the glass, use tweezers to design and arrange glass.

Any glued projects must be BONE DRY before firing or you WILL damage your kiln! Use only white glue such as Elmer's glue.

The shelf paper should be big enough to allow a good margin around your glass piece. The glass piece should be small enough to allow the shelf paper to have a good margin around it. Place glass in the center of it, put the top on and very carefully place it in the microwave oven. Careful placement is necessary to prevent your project from moving around inside the kiln. Do not slam the microwave oven door: close it gently. Gluing pieces together with white glue helps, but the glue must be bone dry before firing. Wet glue creates steam, and steam can damage the black granular lining in the top.

It has been suggested that you will have more control over firing glass if you preheat the kiln with the glass inside on defrost for two minutes before you do a full fuse. I have also seen directions where projects were fired the entire time at 50% power (meaning the microwave oven runs at 100% power but it is turned on only half of the time). Of course, firing times are longer.

Another source suggests prefiring 10 to 12 minutes at 40% or 50% power and then continuing with a regular firing schedule to achieve a full fuse. This method helps prevent shattering.

Because the microkiln absorbs radiant heat, the outer edges of your glass will melt faster than the center.

I have read that different brands of glass melt at different temperatures, too. Wasser melts before Spectrum, Spectrum melts before Bullseye, and Bullseye melts before Wissmach. Your results might be most satisfactory if you use one brand of fusible glass.

Generally, the maximum depth of an unfired, layered glass pendant should be about 1/8 ". More or less depth may change the size and depth of the piece. A project of two layers of thin glass will reach the desired "look" before a project made with two layers thicker glass. Make necessary adjustments to your firing schedule based upon the sizes of your materials.

Do not stack glass higher than the equivalent of one double roll piece (1/8") plus one thin roll piece (1/16") OR three thin roll pieces (3/8"). If you do, puddling may result and glass may stick to the base and sides of the microwave kiln, fusing the top and bottom together.

Ordinary fusible glass melts around 1425F. Dichroic glass melts around 1650F.

Once you have determined how long your project takes, you can put it in and let it fire for the total time. But you will only know that through testing YOUR microwave kiln and YOUR microwave oven.

Molten glass can "crawl". If it should crawl off the shelf paper wait until it cools before attempting to remove it. Molten glass can damage the sides and base of the microwave kiln, so leave enough clearance between your project and these surfaces. Repair kits and replacement bases are available if needed.  

What causes sharp edges on the project? Dragging is usually caused by over firing a project that is resting on fiber paper. As the glass contracts and draws in on itself, the paper resists. Sharp edges are the result. You can reshape the piece with your grinder and fire polish in the kiln.

What causes shelf paper to stick to the project? Most likely it is caused by overfiring; the glass begins to "crawl" and pull on the shelf paper. My observation is that it most often occurs when a  piece of Bullseye shelf paper has been reused and the project was overfired. You can try to remove stubborn patches with cleaning products used to remove hard chemical residue. You can grind traces off and then fire polish in the kiln. A second theory is that the piece was not bone dry.

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One microwave kiln manufacturer recommends a somewhat different firing procedure. The advantage to this procedure is that the microwave is set on medium power, which certainly must be beneficial to the life of your kiln, but the firing time is a little longer. This method is certainly worth testing.

The estimated firing time for an 800 watt microwave oven on medium power is around 6-8 minutes for the small kiln.  From there, start experimenting with short times until you see the orange light. If the piece does not fuse satisfactorily, you can fire it for a longer time.

If the oven's power is less than 500w or if you don't see the orange light coming out through the peephole after the established time, fire the piece for a longer time, heating one minute at time, until you get desired result.

This same brand of microwave kiln actually has a microwave kiln kit which contains finished sterling silver bezels which you fill with small pieces of glass and the entire thing is placed inside of the microwave kiln and then into the microwave oven.  But, when I used my own piece of sterling silver wire and placed it between two pieces of glass and fired at FULL power, the glass shattered and the microwave oven "buzzed". So, I don't recommend doing this unless you fire at medium power.

Alee Soderman's "Cut Cook & Create" book which was published in 1989 states: "The glass shatters while fusing. This is called thermal shock and results from heating or cooling your glass too quickly. Preheat your projects on the low or defrost cycle before cooking them on high. You may have to adjust your cooking time or use medium power if your microwave oven is more than 700 watts."

I am developing a list of general tips for glass fusing glass jewelry. You can see them here: Jewelry Tips.

PRECIOUS METAL CLAY (PMC), ART CLAY SILVER, AND OTHER METALS

Art Clay Silver supplies are available here.

Firing times will depend on the wattage of your microwave oven.

Regarding the "Art Clay Silver" document: PLEASE NOTE UNDER #3 WHERE IT SAYS, "HEATING TIME WOULD TAKE LONGER IF THE WATTAGE OF THE MICROWAVE IS LESS THAN 500 WATTS...." This also means that if your microwave's wattage is more than 500 watts that your beginning firing times should be less than the times shown in the chart below. 

I am awaiting more information about using how to use copper in the microwave kiln.

The inside of the microwave kiln reaches very high temperatures up to 1652 F. Notice the melting point of these metals: (Glass melts around 1425 F).

THE FOLLOWING INSTRUCTIONS ARE FOR SILVER CLAY:

Prefiring test: To avoid melting from over firing, do a test firing with 1 gram of flattened, DRIED clay. Draw a line around the outside of your unfired piece, then fire. If the contraction is 8 to 10%, you successfully fired the piece. If art clay melts, shorten the time. If it crumbles, add more time. PMC will shrink about 10%. If you drop it from a height of  about 2" above a table and you hear a metal sound, it has been successfully fired. If not, fire again with less time.

If you have never worked with precious metal clay or silver clay, PMC3 might be your best choice. PMC3 has minimal shrinkage and fires at a very low temperature which is very good for your kiln. You can also use certain stones and enamels with PMC3.  PMC+ requires a much higher firing temperature and longer firing times. NOTE: I do not recommend putting stones in a microwave kiln as I have never tested them.

PMC3 is best suited for glass applications due to its lower firing temperatures. It is recommended for rings, charms, and pendants. It fires in 10 minutes at 1290 F or 30 minutes at 1110 F** in a traditional kiln. I decided to work with PMC3 because of the lower firing temperatures, which means shorter firing times. The firing process leaves a metal that is less dense than conventional sheet or wire. This means that a piece of jewelry made of PMC is lighter than the same piece made via traditional fabrication; therefore, PMC is not recommended for applications such as findings.

I personally have not yet tested Art Clay Silver to determine what the differences are, if any. Using microwave kilns require EXPERIMENTING!!! But I would recommend that you use whatever formula requires the lowest firing temperature.

Fashion your piece using your fingers and tools, let the project thoroughly dry, fire your piece, and finish by sanding and polishing. (Your piece must be completely dry or it will be deformed. It will also damage your microwave kiln!)

When firing a 3 dimensional piece, support it with a soft ceramic fiber blanket to prevent collapsing under its own weight.

What is the clay volume limit for firing a 3 dimensional piece? Less than 30 grams (which is 1.05 oz). Microwave kilns are not recommended for hollow pieces.

Size Limitation: Small microwave kiln: less than 4 cm (1 1/2""). Do not fire anything larger than this or it will melt.

The size/weight of your project has everything to do with the firing times. Most instructions say to watch for the orange light to appear, turn the microwave off and immediately refire to desired firing time (Use the table below).

Approximate firing time for Art Clay Silver in small microwave kiln:*****

     3 grams (which is .1058 oz)                                    1 to 1.5 minutes
     3 -10 grams   (which is .1058 oz - .3527 oz.)         1.5 - 2 minutes
     10 to 30 grams (which is .3527 oz  - 1.0582 oz)    1.5 - 2.5 minutes
     rope shape or thin piece                                         1 min to 1.5 min.

You will notice that the surface of the fired piece is white. This is due to a crystallization of the silver powder. I remove the powder with a small brass brush.

Silver cleaning solution: sterling silver contains copper and when it gets into high temperatures, it develops a black covering, called fire-scale. To remove it you can mix 1/2 cup warm white vinegar and a tablespoon of salt and soak the piece in it for 20-30 minutes. Note: do not use the stainless steel tweezers with this solution.

This seller is a glass artist and has not experimented with ceramics. The following instructions are compiled for your convenience.

Mr. Ludwig's linked contribution also has directions for firing ceramics.

It is possible to fire ceramic all the way from greenware through bisque to glazed pieces. Here are two cautions for you. First the greenware must be FULLY dried because if you put a piece of ceramic that is even slightly damp on the inside into a microwave kiln it will explode and splatter clay all over the inside of the microwave kiln. This does not damage the microwave kiln but it is messy and obviously you lose the piece. Second if you are going to bisque fire in the microwave kiln it takes almost twice as long as the glaze firing and you still have relatively soft (underfired) bisque. This can create little bubbles in the decoration when you fire the glaze and it also makes for a relatively weak finished product. I recommend using bisque that has been fired in a regular kiln firing because it works better and more reliably. However if you have to bisque fire in the microwave kilns it can be done taking note of the 2 cautions above (i.e completely dry the piece and bisque fire twice as long as your decoration firing time).

Store your microwave kiln in a DRY place. If it has absorbed moisture, dry it thoroughly and then do an empty fire (1-2 minutes) before using.

Moisture will damage your microwave kiln. Your projects and all glue must be BONE DRY before firing!

Use the lowest firing temperatures and shortest firing times possible. Underfire rather than overfire. You can always go back and redo what didn't work and add more time until you get it right.

Do not open the microwave kiln while the outside of the kiln is still hot. Wait 20 or 30 minutes before opening it. Thermal shock will lessen the effectiveness of your kiln AND it is unsafe to open it while it is so hot.

Don't allow your project to touch the interior sides of the microwave kiln. Leave plenty of clearance for glass to "crawl".

If at any time you see tiny cracks on the inside black lining, these can be repaired with the "Repair Kit". Development of tiny hairline cracks in the lining is normal and they do not interfere with the container function. If you should see a bright white light inside the Microkiln when you turn on the oven, the container won't heat uniformly, so we suggest that you repair any crack following the Repair Kit instructions.

Longer firing times are required as a microwave kiln ages in terms of use. Repair kits can be used to rejuvenate a microkiln. Larger microkilns take longer to process a project than small one.

Replacement bases and repair kits are available from this seller.

Periodically visit www.microwavekiln.com to view updates to this information and other products that are available for your microwave kiln.

AND HAVE A LOT OF FUN!!!!