Can You Put Metal In A Microwave Kiln?

Microwave ovens and kilns are both common household appliances used for cooking and crafting. Microwave ovens use microwave radiation to quickly heat food, while kilns use heating elements to bake clay objects like pottery at high temperatures. Some crafters have discovered that placing small kilns inside microwave ovens allows for faster firing times. However, there are risks associated with putting metal objects in a microwave. This article provides an overview of how microwave ovens work, the purpose of kilns, and the safety considerations of using a microwave kiln.

The goal is to inform readers about the feasibility and potential hazards of using a microwave oven to fire kilns. Key questions covered include: Can metal be used safely in a microwave kiln? What dangers are there? What are the best practices? By the end, readers will understand the benefits and drawbacks of microwave kilns to determine if a microwave kiln is right for their needs.

How Microwaves Work

Microwaves heat food by vibrating water molecules inside the food. They do this by producing electromagnetic waves that interact with the polar molecules in food.^[1] When the microwaves enter the food, they cause the polar molecules like water to rotate back and forth rapidly. This molecular movement creates friction and heat, which cooks the food.

Metals are problematic in microwaves because they reflect microwaves instead of absorbing them. The electromagnetic waves bounce off metal and can’t penetrate inside to heat up the food. This is why metal pans or aluminum foil cause sparks in a microwave.^[2] The waves have nowhere to go and instead ricochet around the interior, potentially damaging the appliance or causing a fire hazard.

^[1] https://www.whirlpool.com/blog/kitchen/how-do-microwaves-work.html
^[2] https://www.scientificamerican.com/article/how-does-a-microwave-oven/

Dangers of Metal in Microwaves

Putting metal in a microwave oven can be extremely dangerous due to the risk of sparking, arcing and potentially catching fire. Microwaves function by generating electromagnetic waves that cause water, fat and sugar molecules in food to vibrate rapidly, producing heat. However, metal objects like aluminum foil, utensils, and cookware reflect microwaves instead of absorbing them (Source). This can lead to sparks and electrical arcing as the microwaves bounce around.

The sparks caused by metal in a microwave can damage the interior, especially the magnetron which produces the microwaves. But more concerning is the fire hazard posed by this sparking. If sparks come into contact with any food or grease residue in the microwave, it can easily ignite and result in a dangerous fire. Even small pieces of foil or metal trim can cause sparking and safety issues if accidentally microwaved.

Manufacturers strongly warn against putting any metal in the microwave. The user manual for most microwaves explicitly states that only microwave-safe containers should be used. Any metal cookware, aluminum foil, utensils with metal trim or gold/silver leaf dishes should be kept far away to avoid potential fire, damage and injuries.

Kiln Construction Materials

Kilns are typically constructed from materials that can withstand high temperatures, such as ceramics, glass, and paper. According to Kiln Building Supplies, the most common materials used are firebricks, ceramic fiber blankets, and kaowool ceramic fiber board.

Firebricks made of refractory ceramics are stacked to form the kiln chamber walls, floor, and roof. Ceramic fiber blankets line the chamber as insulation. Kaowool boards are also used as insulation between the bricks. These materials can withstand temperatures over 2000°F without melting or degrading.

While metals like stainless steel can resist high temperatures, they are not commonly used in kiln construction. Metals are prone to oxidation and corrosion at high temperatures. According to Vitcas, lightweight ceramics are favored to reduce cooling time after firing.

The exception is nichrome wire, which can be used sparingly to create heating elements for electric kilns. But in general, ceramics, glass fiber, and paper-based materials are the preferred construction materials for kilns of all types.

Why Metals Are Problematic in Kilns

Metals can cause issues when used inside kilns due to their conductive properties and uneven heating. Metals absorb heat faster than ceramic materials, creating hot spots in the kiln that lead to uneven firing (https://www.reddit.com/r/Pottery/comments/sbbdma/metal_in_the_kiln/). The varying hot and cool zones caused by metal pieces lead to cracks and breaks in ceramic work.

Additionally, when metal heats up, it can arc or release electric sparks if it comes into close contact with the heating elements. This arcing can damage the heating elements over time as well as mark or melt areas on clay pieces (https://community.ceramicartsdaily.org/topic/14240-metal-and-arcing-in-an-electric-kiln/). Copper wire, nichrome wire, and other metal materials are prone to this arcing damage inside a kiln environment.

For these reasons, most kiln manufacturers recommend against using bare metals inside electric kilns. The uneven heating and arcing can lead to disappointing results and accelerate wear on the kiln itself.

Specialty Kilns with Metal

Some specialty microwave kilns do contain small metal components such as nichrome heating elements. Nichrome is an alloy of nickel, chromium, and often iron that is resistant to high temperatures. In microwave kilns, nichrome wire coils are sometimes used to help distribute heat evenly within the kiln.

However, precautions are still needed when using these kilns as the metal is intentionally limited. The nichrome elements are typically encased or shielded so they do not arc or spark when exposed to microwave energy. Care needs to be taken to ensure any metal wires or coils are properly insulated and contained within the kiln’s firing chamber.

It’s also critical to carefully follow the manufacturer’s instructions when using a microwave kiln with any metal components. Do not modify or tamper with the kiln which could expose the metal wiring. Use the kiln only for the recommended purposes and materials to prevent unsafe conditions.

While it’s possible to have small controlled metal pieces in specialty kilns, microwaving any standard metal object remains hazardous. So microwave kilns with nichrome elements require precautions but can enable products requiring more specialized heating.

Alternatives to Metal

Many ceramic kilns and kiln components are designed to avoid the use of metal. Common alternatives to metal in kilns include:

Ceramic – High alumina ceramic materials are extremely heat resistant and can withstand temperatures well over 2000°F (1093°C) inside a kiln or furnace. Ceramics like 99% alumina are ideal for kiln furniture, posts, props, and other non-metallic kiln parts.

Silicon Carbide – This extremely hard synthetic material can withstand heat up to 4200°F (2760°C). Silicon carbide kiln shelves, batts, and furniture are resistant to thermal shock. Silicon carbide elements are also used in some electric kilns.

Other non-metallic options for kiln construction and parts include quartz, cordierite, mullite, and some specialty composites. These provide alternatives to metal that can withstand the high heat inside ceramic kilns during firing.

Carefully choosing non-metallic materials for kiln construction, furniture, props, and firing accessories allows firing ceramics safely at high temperatures while avoiding potential metal-microwave interactions.

Tips for Safe Use

When using a microwave kiln, it is crucial to avoid any metal objects inside the kiln chamber. Metals can lead to arcing or sparks inside a microwave, creating a fire hazard. According to Microwave Kiln Basics and FAQs – Before You Buy, you should never touch any part of a microwave kiln with bare hands unless you know it’s cool, as the metal lid can get extremely hot.

Only use materials rated as kiln-safe inside a microwave kiln. Certain materials like paper, plastic, and fiber blankets can burn or melt at high temperatures, as noted by Things To Consider Before Buying A Microwave Kiln. Carefully check manufacturer instructions about approved materials. Use high-temperature rated kiln shelves, posts, and furniture meant for microwave kilns. Avoid any unknown materials that could interact with microwaves in unsafe ways.

Example Projects Using Microwave Kilns

Microwave kilns can be used for a variety of hobby projects and small-scale artwork. Some common example projects include:

Ceramics

Microwave kilns allow ceramic artists to fire small pieces of pottery, tiles, and sculptures. The quick heating allows for rapid prototyping and testing of glazes and clay bodies. Small ceramic pieces like jewelry pendants, beads, and mini figurines can be conveniently fired in a microwave kiln. According to this beginner’s guide on warmglass.com, fired ceramic pieces will be food-safe and durable if properly fired to the manufacturer’s specifications.

Jewelry

Jewelry makers often use microwave kilns for fusing and annealing precious metals. According to this Pinterest board, pieces like silver rings, copper bangles, and fused glass pendants can be fired in a small microwave kiln. The quick heating works well for soldering and fusing small jewelry components.

Glass Crafts

Fused glass artists can use microwave kilns to fuse glass together into plates, coasters, and small sculptures. According to warmglass.com, proper firing schedules are important for achieving the desired results without cracking or breaking the glass. Microwave kilns allow glass artists to rapidly test color combinations and patterns.

Conclusion

In summary, traditional microwaves and metals absolutely do not mix. Microwaves work by generating oscillating electromagnetic waves that cause water molecules in food to vibrate and create heat through molecular friction. When metal is introduced into a microwave, it can reflect these electromagnetic waves and cause arcing, sparking, and fires. Metal objects in a microwave can also become extremely hot and potentially explode.

For these reasons, metal should never be placed in a standard kitchen microwave. Microwave kilns utilize special construction and designs to isolate any metallic elements and prevent them from reflecting waves. While specialty kilns with metal exist, it takes precise engineering to avoid the risks. For most hobbyists, it is best to stick to microwave-safe materials like glass and ceramics when crafting in a home microwave. With care and caution, microwaves can be used safely for small projects without metal. But in general, metal and microwaves simply do not mix.