The Copper Matte Raku Technique Adil Ghani

Appears in the Jan/Feb 2023 issue of Pottery Making Illustrated.

I founded the ceramic art brand RAAQUU to make the magical world of raku ceramics more accessible to ceramic art enthusiasts all over the world. A raku specialist for more than 15 years, I make decorative ceramic home decor, vases, and sculptures under the RAAQUU brand. 

Raku ceramics are special because of the unpredictability of the raku firing technique. Raku firing consists of heating the ceramic piece to the temperature required to melt any glaze on the surface, then removing the piece from the kiln while it is still red hot and any glaze is molten. The iridescent rainbow colors come not from glaze but from a post-firing reduction process acting on the copper-matte glaze. The color actually comes from copper metal reacting to the absence of oxygen.

Immediately after coming out of the kiln, the ceramic piece is placed in a reduction chamber—usually a simple metal bin—filled with sawdust or paper. The extreme heat from the ceramic piece ignites the combustible material in the reduction chamber, which is then sealed for a while. What happens next inside the chamber is the key to the unique and unpredictable colors and patterns of each raku ceramic piece.

One of the reasons that I decided to explore raku was because I had very limited resources and had to truly be economical in deciding which technique to invest in. I chose raku also because it is not a popular technique in my home country of Malaysia and thus, I believed that there was great potential for growing this technique here.

My Cause

Throughout my journey as a ceramic artist, I have found that awareness of raku-fired ceramics is very low, even among the ceramic-enthusiast community. Most raku work is made by individuals as a hobby, rather than commercially since the complex raku process must be carried out one item at a time and can still lead to inconsistent results. This narrow field limits the awareness of raku firing and accessibility to the type of work. 

I hope to increase the understanding and share the excitement that comes with the raku firing process with all of you.

Hazard Warning:

• If you are sensitive to smoke, the raku-firing technique used in this project can be physically hazardous. Always wear a properly fitted NIOSH-approved respirator with the appropriate filters.
• Use only high-temperature, heat-resistant gloves that are rated to at least 1700°F (930°C) and made for use in a ceramics studio. Oven mitts are NOT safe.
• Pieces may fall out of the reduction cans while the temperatures are well over 1832°F (1000°C). Though they may look cool, please ensure that you are wearing ALL appropriate safety gear and that you use tongs to touch pieces.

Materials and Equipment

• Raku kiln

• Bisque ware (1) made from thermal-shock-resistant clay such as earthenware

• Copper Matte Glaze (see recipe on page 37)

• Soft paintbrush or ladle

• Safety gear: Dust mask or respirators (preferably N95 rated), ceramic-rated heat-resistant gloves, safety goggles, hair ties, closed-toe shoes

• Small metal cans (at least 6 inches in diameter)
  with lids

• Ceramic-rated tongs

• Old newspaper and sawdust

• Bucket of water, for safety and to cool ware

• Plenty of space free from anything flammable

• Two other people to help during the raku firing phase

Applying the Copper Matte Glaze

First, either mix 240g of RAAQUU Copper Matte Glaze Mix powder (available from RAAQUU, inquire at inquiry@raaquu.com) (or use the Generic Copper Matte Glaze recipe) with 300ml of water to create a black solution. 

Next, using a soft paintbrush or ladle, paint the bisque ware with the glaze (1, 2). You may also dip the bisque ware into the glaze for a smoother finish, provided that the vessel or bucket containing the glaze is large enough. I try to create an organic patten of streaks that overlap on my signature Koban Vase. Note: The RAAQUU Copper Matte Glaze and the Generic Copper Matte Glaze have a low melting point, and they will mature in about an hour.

The Raku Copper Matte Firing Technique

Once the glazing process is complete and the glaze is dry, load the kiln and bring the temperature up to 1832°F (1000°C). This should take about an hour. I use a pyrometer to ensure I am at the correct temperature (3).

Check on the ware every 15 minutes or so after you’ve been firing for about 45 minutes. Look for bubbling in the glaze, and once it starts bubbling, you are about 15 minutes away from the time to remove the ware from the kiln. You know your ware is ready to pull out when it is glowing red, and the glaze surface appears shiny and liquid.

While you’re waiting for the glaze to mature, you need to prepare your reduction chamber. Shred some newspaper and fill several small metal cans with it (4). The cans should only be a little bigger than the pieces you want to put in them, the smaller the better to create a good reduction and lots of pretty colors.

Once the pieces are ready (5), you are going to need three people to start the next stage of the process—one to open the door, one to pull the pieces out with tongs and place them in the cans, and one to close the can lids. Each person should already have their own set of gloves, respirator, and safety goggles on for protection. 

Person one opens the kiln door or lid while person two pulls the wares out, one at a time (6). The door should be closed between pulls to retain heat within the kiln. Place the wares as quickly as possible into the waiting cans (7). As soon as the shredded newspaper catches fire (8), person three should fit the lid on securely to smother the fire and smoke the pieces (9).

After the lids are secure, wait a few minutes for the fires to smother and smoke the pieces. A good seal in a well-formed reduction can will not emit any smoke. Look out for signs of leakage where there is smoke coming out of the sealed can. Also, be careful when you open them up. Keep a safe distance as you remove the lids and watch out for back drafts.

Remember that once removed, the wares are still EXTREMELY HOT! Any remaining shredded newspaper will begin to burn again once air is introduced back into the can. You can pour some water into the cans to put them out and cool the ware. Once slightly cooled, you may take the pieces out with tongs or ceramic-rated gloves (10) and douse them in the bucket of water or allow them to cool naturally. 

After the raku piece has cooled, you can remove any sediments, carbon, and debris using a sponge and water. 

Final Thoughts

Now that you have fired your first raku piece, I would like to leave you with a few insider tips to help you on your journey. 

Firstly, if you are unhappy with the colors that are produced during the reduction phase (in the can), the raku piece can be refired and reduced again until you are satisfied with the colors.

One of the risks of raku-fired pottery is that the glaze surfaces on the pieces oxidize over time. Choosing the right sealant will protect your piece from oxidation and retain its coloration for years. You can purchase a sealant from your local hardware store. Make sure the sealant contains UV protection and be sure to test it before applying it to your pots as many sealants will darken/oxidize the raku surface instead of protecting it. Finally, note that raku process does not produce a vitrified surface, therefore pieces tend to be porous and are not food safe.

There are numerous different raku techniques to be explored besides copper-matte raku such as horsehair, smoked, saggar fired, obvara, pit fired, and more. You have a world of unlimited possibilities with your new raku technique.

Adil Ghani is a ceramic artist in Malaysia, who specializes in raku-fired pottery. His award-winning pieces are handmade in his 5 signature raku finishes under the RAAQUU brand. With a global presence and collectors in more than 30 countries, Adil hopes to bring greater awareness to the raku technique worldwide.