I’ve been getting a few questions on my YouTube channel regarding making functional raku pottery, such as mugs, cups and bowls. There seems to be a lot of information (and misinformation) around how to make raku pottery waterproof and/or food safe. While I’m no expert on raku pottery, I have picked up a few helpful tips along my ceramics journey.
What is Raku Pottery? Raku is a Japanese style of pottery introduced in the late 1500s. The practice involves removing red hot pieces from a kiln and dunking them into water or a reduction chamber filled with combustible materials, for example, paper, sawdust or dried leaves. Some artists will even use horse hair to create intricate patterns over pots and vases. This rapid cooling of the pieces is what produces the unique crackled surfaces seen in some raku-fired pieces.
This in turn leads us to one of the most commonly asked questions: is raku pottery food safe? The short answer is always “no”. Some people will argue that you can seal the pottery after firing to make it waterproof, but a traditional raku-fired piece will not withstand the everyday use of a functional object.
While it’s true that raku pottery includes the popular “tea bowls” for consuming liquids, the function of these bowls was very different to our modern-day tea and coffee mugs. These bowls were used during special tea ceremonies and the liquid did not sit inside the vessel for too long. As raku pottery remains porous after firing at lower temperatures (and often with crazed/crackled glaze), the vessel can absorb some of the liquid and not only cause stains but “sweat” right through the porous ceramic material. This is what happens when the clay is not vitrified (cooked) at moderate-high temperatures, to help close the surface pores that make our modern-day cups and mugs waterproof. To make “functional waterproof” pottery, you need a combination of stoneware or porcelain clays with higher heat (around 1200-1270 degrees Celcius). Also, these raku tea bowls would not have been washed after use with harsh detergents. They would have only been rinsed, dried and placed back on the shelf until the next tea ceremony.
Can’t I just use a Stoneware Clay and Fire Hotter? Again, the answer is no. Raku is fired at a lower temperature specifically to achieve those dramatic surface changes. Most would recommend firing around 700-900 degrees Celcius (I have had success firing up to 1050). Firing too hot and closing the pores will reduce the chances of Raku-specific glaze reacting as they should. Raku glaze is also a “low fire” glaze that reaches an ideal melting point at much lower temperatures, they will run and make a big mess if over-fired. The trade-off is a uniquely patterned, porous vessel that can be polished with wax to help seal the exterior further – but won’t create a watertight vessel for your morning brew. Below are some examples of my decorative raku-fired pieces, available for purchase in my shop.
Can I Eat from a Raku Vessel? Many old-school raku glaze recipes contained lead, making them toxic for any food or drink consumption (artists such as Charles Goldie who licked their paintbrushes into fine tips, sadly succumbed to lead poisoning!) However, today’s modern glaze options allow us to source “food-safe” glaze for raku-specific firings. Check the manufacturer labels for specifics. If the label says food safe, then YES, you can safely consume “dry” foods from the vessel. Also as a rule of thumb, never lick your glaze brushes 😉
Why only Dry Food? Raku glaze has the tendency to crack or craze. This allows food particles to get into these cracks, which can be difficult to clean and in turn, can lead to bacteria growth – yuck! So it’s best to stick to dry foods only. The dramatic temperature changes during raku firing, and specific glazes used, are what create those desired crackle effects. There could also be hairline cracks that run right into the pottery (again, pretty normal for raku pottery)
Now that we have discussed traditional raku and low-fire methods of firing (usually DIY gas kilns or small pit fires under 1000 degrees Celcius), let’s talk about how you CAN achieve functional and waterproof “raku style” pottery.
Modern glaze options are endless! We now have access to midfire/stoneware crackle glaze (I would recommend just using this on the outside of functional ware and a nice smooth gloss glaze inside) and iridescent glaze that can mimic similar effects of copper raku and other colourful glaze achieved via reduction chamber process. Amaco also has a great website that offers a wide range of glaze combinations to create unlimited surfaces:
Another option to achieve smokey and unpredictable effects similar to raku (minus the bright colours or crackles) is to look at soda firing, wood firing and large pit firing. These firing options produce amazing, organic looking pieces in earth tones but it comes at a price. Soda firing releases chemicals that are damaging on kiln elements and insulation, meaning parts will need to be replaced more often. Pit and wood kiln firing can take days and a tremendous amount of wood and space to operate.
I hope this has helped answer some questions around raku pottery and if this style of firing is the right option for you.