Using the Raku Process to Show Oxidation-Reduction

A little while ago, I went looking for a video to explain the oxidation/reduction aspects of raku so I could assign it for my students to watch while I was out of the classroom for a day.

Sadly I didn't find one, but I did come across this video from the inaugural ASM teacher camp in Butte, Montana. It doesn't explain the redox aspects of raku - though the title suggests that it might - but it does include your friendly, neighborhood blogger in his orange polo shirt (ASM-branded, natch), and jeans.

Because the video doesn't explain the science, I'll give a quick version...

• We use a clear glaze into which we mix oxidized metals (cobalt oxide, iron oxide, copper carbonate, nickel oxide, etc). Each glaze gets just one of those oxidized metals.
• The pottery is taken out of the kiln while it's hot - somewhere around 1050 ^oC. At that point the glaze is molten, allowing oxygen to leave the glaze.
• The hot pottery is placed into a metal can with something flammable. In this situation we're using torn up newspaper.
• The torn up newspaper catches fire and starts to consume the oxygen in the now-sealed can.
• The carbon and hydrogen from the paper continues to 'search' for more oxygen, so it reduces the metal in the glaze and takes the oxygen from the oxidized metals. (This only works if the pot is hot enough for the glaze to stay molten in the reduction environment.)
• The glaze cools, sealing in the now-reduced metal within it, leaving - hopefully, if everything works right - reduced, shiny metal in the glaze.
• The pottery is quenched in water to lock in the final version of the metal within the glaze - either reduced or oxidized metal.

You can see lots of versions of raku pottery on other blog posts.

Raku firing

Not a lot of science in todays' video.

In fact, there aren't even any words in the video - either recorded diegetic or narrated after the fact.

Instead, we just get some stunningly gorgeous raku pottery from an outdoor kiln.

We can see the fully oxidized, green of the copper glaze and the stunning, reduced copper after the quench. 

The Clay Collective published three videos. I've put the prettiest one up above, but the other two are worth seeing, as well. 'Round 3' shows them setting up the kiln initially, and 'Round 2' shows pieces that didn't get nearly the reduction that they got in the video above (assumedly, 'Round 1').

Raku man, who knows what you're gonna get?

Alcohol Reducation Raku with Shawn Felts

Raku is pretty stunning.

I don't know that we need another raku video on this blog, admittedly, but there's something unique here that's worth seeing.

• I very much dig that the video here opens with a comment that Shawn Felts worked at Funke's Fired Arts (the ceramics store here in Cincy that we use for our supplies at Princeton HS). They've changed ownership and names since Shawn worked there, but they're still a good place.
• There's a whole lot of talking to start the video meaning it's really informative, but it would be awful to show in class. There's no way that students are going to pay attention until probably 19 minutes in - when the fire starts.
• I appreciate the full beard and the confidence with it around the fire.
• At about 13:40 he mentions that raku pottery all fades to black (oxidized) over time. I've not noticed that in the past, though I've only done raku for about a half dozen years. Is that fading anything that anybody has seen in their experience? I think our glazes might encase the reduced metal in a thicker glass layer, so that may not be the case for our process.
• Holy crap that furnace ramps quickly. He goes from room temp to 1750 F in about twenty minutes. That's a fast, frickin' ramp rate.
• So much of this seems like he's doing it because he's done it before and it worked. Comments like that the alcohol 'soaks into' the glaze make me think that the science is a little iffy in some of his explanations.
• It's at about 18:50 that the piece finally comes out of the kiln. 
• I'm still very much unsure of how the glazes work and all the science of raku. With my understanding of the science, the repeated sprays of alcohol are doing almost nothing because it's just burning off each time. Yes, oxygen is being used up and copper is reducing, but that is immediately lost when the hot pot is allowed to then sit in the air before being moved into the sand under the glass bowl.
• The glass bowl is the big reason why I'm posting this video. We actually get to see the reduction (at 21:15 with the last shot of alcohol into the reduction chamber), something that we never get to see because our reduction chamber is entirely opaque (metal paint cans.)
• I appreciate Shawn's impatience, something he mentions at 25.45...and again at 28:05.
• I wonder how much the time jumped at 24:15, because there's a clear edit. How long was the piece in the reduction chamber cooling down?  
• Can we talk Bernoulli's Principle when he blows the air in at 24:44?
• Holy crap...the color change right after the blow of air is a great money shot for the video. Actually seeing the reduced copper (shiny penny) change to oxidized copper (shiny blue, purple, green) is stunning.
• Does the spray with water just cool the glaze enough to not allow oxygen to move into or out of the glaze? That's my understanding but doesn't quite fit with Shawn's explanation.
• More edits at 26:14...27:30...30:35...31:35
• Who are the people watching this video? They don't look like they're dressed to get involved. Maybe this is just an open house situation.
• I never knew what grog was (28:40). I knew our raku clay had a bunch, and I kind of knew why (decrease thermal shock). I just never knew what grog was - already fired, pulverized clay so it doesn't shrink. 
• Shawn mentions at 28:50 that he could dunk the raku piece in water without it shocking but almost chuckles as if he wouldn't want to risk it. Hey, that's exactly what we do with our pieces.
• Some alcohol jokes at 30:10 - talks about the fumes tasting like rubbing alcohol and that Shawn's more a bourbon man than he is a rubbing alcohol man.

Artistic Chemistry: a beuatiful collaboration

I'd never heard of Frog Valley before reading the April 2012 Chem Matters article, "Artistic Chemistry: a beautiful collaboration," and to be quite honest, the article didn't exactly tempt me to drive six and a half hours to see an artist collective. As the last paragraph of the article says, "you may want to try raku pottery or stained glass. Classes are offered throughout the United States, and chances are, classes are available near you." 

Apparently there's no reason to go to Frog Valley. Thanks, Helen Herlocker.

The other part of that last paragraph, though, "while you learn about the properties of the materials and how they interact with each other, you will discover that it really is all about chemistry!"

The article covers the science of raku pottery (oxidation, reduction, metals, and metallic oxides) as well as the copper foil method of making stained glass windows (chemical reactions, production of hydrochloric acid, tarnishing of the copper foil).

Plus you get to see some really pretty artwork.

Get out there and take a class this summer, folks. Make a stained glass piece (don't leave it out for your custodian to knock over like I foolishly did with mine). Throw a raku pot. Blow glass.

Learn something.

Make something beautiful.

Alcohol Raku Firing of a copper matte glaze with alcohol reduction

I am seriously terrified by the use of alcohol as the combustible material for the raku process. I've posted a video and said as much before, but there's a reason for this post beyond just the use of alcohol as the combustible material and the lack of proper safety equipment (no safety goggles, shorts, Crocs). It's the explanation that appears at 0:58 in the video:

The hottest spots will color up first, so be ready to spray water on spots you want to color freeze. Torch the copper colored areas later and spray water when you hit the desired color [to] freeze it. If you mess up, you can always refire and try again!

Ok, on some level I've understood that the reduction of the metal oxides is favorable at high temperatures (we discuss that in AP chemistry as it relates to thermodynamics and Gibbs free energy, and we show it in material science when we demonstrate the copper sheet), and I even knew that the process was reversible because of that demonstration. I never thought to apply that to raku, however.

The reduction in raku happens best with the first few pieces pulled from the kiln because they're the hottest ones. The cooler ones are on the verge of being too cool for the reduction to take place. That's shown in the rainbow of oxidation that appears at 2:47. The oxidation builds back as the piece cools until the glaze is cool enough to lock the color in and not allow any more oxygen into the metal/metal oxide system. There's a sweet spot of temperature above which reduction happens, below which the glaze is set and neither oxidation or reduction can happen, and during which oxidation can happen.

But I never thought to 'refire' the pieces using a torch (5:40)...or to use a spray bottle to quick cool the piece below that magic range and lock in the color (2:40)....or to display my raku pieces in a drained hot tube (6:47).

That's brilliant in its simplicity.

As we hear at 1:48, "it's almost like a science."

Table of Cone Temperatures

Cone temperatures for ceramic firing

When I was in Salt Lake City last summer, I happened upon a small ceramics gallery (Red Kiln Pottery). I was initially looking for some glaze that I had ordered from my Provo supplier sounded a little iffy. At worst, I thought, I would end up with the wrong and the right glaze.

Red Kiln didn't have what I needed but they were able to help me understand the temperature ranges (that we use in our ASM workshops) that correlate to the various cones (that real ceramics folks use to gauge their kiln's temperature). It's a document to which I've referred a number of times, and I thought it might be helpful to share out. 

Thanks, Red Kiln!

Firing Raku Pottery in the Microwave Oven: The Paragon Kiln Operation Series

The Paragon Magic Fuse kiln is available online and from local dealers - there are four within twenty miles on my house. It's only $160 and weighs 5lbs, so I'm guessing the shipping wouldn't be too bad.

There are a few limitations of the kiln - the need for a microwave, the tiny maximum size of the piece being fired - but it is a way for you to do small raku projects without buying a larger kiln.

Plus it's just really frickin' cute!

Raku Pottery

I love watching potters work. Sure, just beat the snot out of that clay square and roll it on through a pasta machine. Later, smack it a while with a wooden spoon. Yup...pottery!

Admittedly the first 3:40 or so of this video is just watching clay getting formed, not that sciency or exciting. Then the furnace opens up, and they reach in with just gloves (at 4:30) to reload the kiln. Sheesh...

And finally, at 9:20, we get to see the finished products...so pretty.

Alcohol Reduction

This one stuns me.

My experience with the raku process comes entirely from Materials Science - either the summer workshops or the class at Princeton High School. That means I'm used to doing raku reduction with pots about as big as an apple or so - and we drop those into a metal can with newspaper and/or sawdust. That's about it. Sure it's a little frightening because of the fire and heat, but it's a controllable situation.

When I mention raku to art teachers, they ask about the outside pit and the fire and all sorts of stuff that exists on a scale far above what I've ever worked with. Then you get to using misted alcohol as your combustible fuel source. That's another level of awesome/frightening entirely.

Plus these folks aren't wearing long pants, close-toed shoes, heavy gloves, goggles, any of the stuff that we use in science class, so I'm a little freaked out.