How to Inlay Glass into Wheel Thrown Raku Pottery

Vessel, 20 inches high. Embedded glass technique glazed with Rogers White with brushes of Del Favero Luster glazes. Slight post-firing reduction. By Steven Branfman.

Placing broken glass inside bowls and platters to melt and pool in the glaze firing can create lovely surfaces with lots of depth (though these surfaces should be tested for food safety). I’d seen that technique used many times to great effect, as well as the technique of embedding little pieces of glass here and there as embellishments on pottery. But I had never seen anyone inlay glass exactly like Steven Branfman does.

Steven throws a cylinder and then rolls it in crushed glass. Then he continues throwing from the inside (so as not to cut his fingers!) to shape the pot. In today’s post, Steven takes us through the process step by step. – Jennifer Harnetty, editor.

COMBINING CLAY AND GLASS

I began incorporating glass into my work about 25 years ago as an effort to unite two apparently similar materials. Clay and glass are at least cousins if they are not siblings, and although clay was the material that I was connected to, glass held a certain interest.

My first efforts involved incorporating the glass as “windows” through the surfaces of my pots, connecting the glass in the fashion of leaded-glass technique with clay cutouts in the wall of the vessel acting as the frames for the cut pieces of flat glass. At the same time, I was using bits of glass as decorative elements by laying them flat inside bowls, dishes, plates, and platters, and allowing them to melt into the surrounding glaze. Combining these two materials proved to be much more difficult than I had thought it would be. These experiments with glass took place along side other work that was proving to be much more interesting and engaging and soon my interest in the glass all but disappeared.


Fired up about raku firing?
Then take the technique to the next level with Raku Firing: Advanced Techniques.


It wasn’t until some years later that the glass idea re-emerged, although from a completely different perspective. From very early, my pots have been about the relationship between the surface of the ware and the form. As I matured as a potter and a maker of vessels, my understanding, interpretation, and representation of the vessel became, and continues to become, more precise, sophisticated, and personal.

How the interior space of a pot shapes, defines, and gives life to what we see on the outside is elemental to how I conceive and make my ware. I form pots from the inside out and the bottom up. And while pressure and force on the outside of the clay during the throwing process is a key element to controlling the shapes and sizes of the forms, it is the inside pressure that I exert that actually creates the pot.

The surface of a pot is more than a simple canvas upon which to decorate or embellish. It is a skin that contains and thus expresses and communicates all of the power within. The incorporation of crushed and inlaid colored glass is yet another method I use to articulate and embody that power.

As with most craft methods, there are many nuances of technique, method, and personal style that are not possible to demonstrate within the limitations of the printed word. Start your experiments with small amounts of clay and simple shapes building up to larger, more complex forms as your skill improves. Don’t be satisfied until you have incorporated this new method into your own language of shape, color, texture and form.

METHOD

There are four steps to the technique:

1.Forming a cylinder

2.Inlaying or embedding the glass

3.Forming the shape by expanding it from

the inside out

4.Finishing the piece.

Although my work is all thrown, with modifications you can easily adapt this technique to slab work.

Step 1

You must throw your form on a bat. Plastic bats that tend to bend are not recommended until you have more experience with this technique. (You’ll see why later.) After using liberal amounts of water for centering and the first few pulls, I dry my hands to throw the rest of the clay completely dry.

Step 2

Note how little water is visible in the photos. Dry throwing leaves the cylinder strong and able to withstand the stresses that the clay will have to withstand later in the process. The cylinder must also be formed with very even walls that are left thick enough for the glass to be embedded and subsequently expanded. Dry throwing is a skill all to itself and one that will take a lot of practice to master.

Step 3

When you complete the forming, the clay should feel somewhat stiff (though not nearly leather hard) and dry to the touch. Depending on how dry you throw, you can put the cylinder aside until the surface wetness dries. If you do that, be sure to maintain even drying, not allowing the cylinder to warp or bend and not allowing the rim to get dry. Tip: Before you lift the bat off the wheel, mark the pins and corresponding holes in the bat so you can put the bat back on the wheel in the same orientation.

Step 4

While the cylinder is setting up, I prepare my glass. I use random varieties of flat, colored glass used by stained glass workers. You can use any type of glass available to you, including bottle glass, marbles, and glass rods. Wrap the glass in canvas and simply crush it with a hammer.

Step 5

On the table I lay out my glass carefully choosing colors, sizes of glass (from large pieces to dust), and the arrangement of the glass in patterns and shapes visualizing how these patterns will transfer to the surface of the clay.

Step 6

The cylinder will be rolled onto the glass, so as you lay it out pay attention to how close to the rim and the foot the glass will be inlaid. You must be able to finish throwing the neck and rim of the piece without touching the glass and then trim the bottom and foot (if you choose to trim) without running the tool over the glass.

Step 7

Holding the bat almost as a steering wheel and supporting the cylinder from the inside, roll the cylinder in the glass. This is where a rigid bat and stiff clay is critical.

Step 8

Place the cylinder upright and paddle the glass into the clay still supporting the clay from the inside to maintain the integrity of the cylinder.

Step 9

Each time the clay is rolled onto the glass, it is to enhance the pattern and the coverage on the vessel’s surface. Repeat this process until the surface is as you want it.

Step 10

The more you roll the cylinder, the more it will become stretched and distorted. Work carefully to minimize the distortion.

Step 11

To combat distortion, gently return the cylinder to its vertical form by grasping the cylinder around the outside, pushing it and pulling it back into shape.

Step 12

In preparation for continuing the throwing process, collar in the top of the cylinder.

Step 13

Throw the top of the cylinder slightly to re-orient and re-center it.

Step 14

If you’ve never done any one-handed throwing, this next step will take some practice to arrive at a comfortable personal approach. The more centered (meaning evenly thrown walls) the cylinder is, the more success you will have in one-handed throwing.

Step 15

I use my left hand inside the form to raise the clay and push it into the shape that I want. Yes, even with only one hand you can still dig into the clay and raise it! Hold and control your left hand and fingers just as you would if you had your right hand also working on the outside. A slow, careful approach works best. I alternate between using my hand and using a rib to expand the shape. Curiously, although I use my left hand inside the pot for throwing, I am more comfortable and have more control using the rib in my right hand.

Step 16

When you use a rib, be careful to hold it as flat as possible (not at a 90-degree angle) against the inside wall so you don’t scrape clay away. The idea is to push the clay outward, not to scrape clay away and unnecessarily thinning the wall. As you expand the wall and it gets thinner, you’ll feel the texture of the glass. It will take practice and experience to learn how much you can expand the vessel before you stretch it too much!

 

Comments
  • Francine S.

    What temperture do you bisque fire the vessel?

    What temperture do you Raku the vessel to?

    Love the technique it will be fun trying.

    Francine

  • Interesting and beautiful!

    I have a similar question: I’ve always thought glass was very low-fire. I’d like to try this with porcelain, if possible. How high can glass, such as bottle glass, be fired to?

    Thanks!
    Heidi

  • Nursen E.

    Colours seem lovely. Technique needs a lot of experience. Thanks for sharing. Nursen

  • Tahany E.

    new technique , i like it ,thanke u

  • Naz B.

    Heidi,

    I use glass on horizontal surfaces in my work.I fire to cone 6. At higher temperatures the reds and oranges will normally burn out, But other colors stay.
    I make pendants with cone 6 porcelain.Any kind of colored glass can be used.

    I hope this helps,
    Nazila

  • Thanks, Nazila, that does help.

    I had always thought that at cone 6, the glass would be nothing but history. 🙂

    I can’t wait to try this!

    Heidi

  • Sheila M.

    I fire ti cone o4-03 and would love to experiment with glass. I also thought a very low firing was needed. Anyone using low fired clay with experience in this? Thanks for your help!
    Sheila

  • Karen S.

    I have used sea glass in the bottom of bowls, plates & platters but never on the outside of a thrown piece. One time someone glued sea glass to the rim of a piece, it splattered all over the place & trashed a kiln shelf. This was/is a community kiln & was not a welcomed out come.

  • Suzan C.

    I fire glass to ^9-10 but only on horizontal surfaces. Greens and blues always come out great. The red and yellow families either turn brown or clear.

    Sue

  • Amanda D.

    I have found that the reds do tend to burn out but it is possible to cheat a little with underglaze colours under the glass to give it a bit more colour in the finished effect.
    I am a little concerned about how much the glass would rin and therefore adhere to the kiln shelf but I guess like most things it is down to quantity used and trial and error.
    Mandy

  • Muriel W.

    I have incorporated glass in my tiles quite often in the past and at temperatures as high as cone 10. Cone 6 does give me a good result. The glass cracks as it cools and makes an interesting surface. Sometimes if the glass is too dense it could chip away after it cools, too thin a layer and it has no more effect than and clear glaze. The depth of the color is good in greens and yellows and can be influenced by the clay, under-glaze, and or slip under it. After reading this article, I think I will try it now on vertical surfaces. Thanks for sharing. Muriel

  • Karen B.

    Thanks Steve. Really nice piece. Love the contrasts within the shape, the color, and the inside-outside.

  • Genevieve N.

    You can look at Mark Hewitt and other North Carolina potters for examples of placing bit of broken glass (blue generally) around the shoulders of big jars etc, and they fire at stoneware temperatures, often in a salt kiln. They impress the glass after throwing. It’s an old tradition over there.

  • Velda H.

    Hi Steve
    Thanks so much for sharing.
    I have researched raku glazes and would
    like to clarify – is Corn Stone- Cornish stone
    also known as petuntze? Our raw materials
    here in Australia are often given different
    names Cheers Velda

  • Velda H.

    Hmmm I understand that its similar to Potash Feldspar … Velda

  • Michelle J.

    I am a 3rd year ceramics student at an Australian University. I have been makinggymnastic typecoil figures which I plan to drape glass over. I have been interedted in using glass with ceramics for some time but everywhere I ask I am told not possible. I have booked in for a workshop with a glass artist in a few weeks and she has warned me that draping glass over figures is unlikley to work. has anyone tried this?

  • Karen C.

    I have been playing with ceramics and clay since ’72. I got into glass about 5 years ago. I am a process person and love to work mixed media. This has always seemed like a natural to me, glass and clay, but all the teachers say that it is too difficult to match the COE’s. So my question is; “Does it really matter as long as I enjoy the results?”

  • Leslie G.

    Hi. I’m going to chime in as a glass artist who started (and occasionally dabbles) in ceramics. Glass COE (coefficient of expansion) is the rating of expansion and contraction when heated. Matching the COE is absolutely crucial when talking about forms/designs that have to maintain structural integrity. For example, if you were to fuse or combine COE 90 (simple Boro, like Bullseye) to COE 104 (soft glass like Moretti, your piece would just crack apart and shatter. Incompatible COE’s can be used in some very specific instances, providing they are used sparingly and strictly in surface design. For example, I have used COE 96 frit (crushed glass) on COE 104 pieces and as ling as the frit has been thoroughly melted in, it can yield spectacular results.

    Now in theory, it seems to me that adding glass with an unknown COE underneath surface glaze in ceramics shouldn’t significantly compromise the integrity of the piece; although you could have instances of pitting, flaking and crackling (all of which might be very desirable if you’re seeking a primitive or antiquated effect.) Note: most commercial glass items are on the low end with a COE ranging from 83 to 87, meaning the melting point for that glass is around 1650 degrees F. That’s about 580 degrees F lower than Cone 6, which means the glass starts to run significantly before the clay body begins to vitrify. Again, it seems that since the Raku process encompasses such wide temperature ranges, you’d likely get some extremely interesting results. However, if you’re adding frit to a piece after it has been glazed, I’d predict it would mostly run/pop off and make a mess on your kiln shelf, and likely pit/scar your glaze. (This is a guess- I haven’t tried this yet.)

    It seems like picking a glass COE that’s roughly compatible with the cone you’re firing, would yield the best of all possible worlds. However, it seems that since we’re only concerned with surface design and not with structural stress, you’d be just fine- so long as your ware isn’t subject to significant temperature changes (such as used on a vessel or piece intended to be microwaved, placed in the dishwasher, or displayed outside.)

    Here’s a link to a site that I find extremely helpful when working with mixed media. http://mikegigi.com/techspec.htm#GLTEMP

  • Leslie G.

    Note to artists using hot palate glass: (Reds, oranges, browns…) Hot colored glasses are notoriously finicky and do tend to burn out when overheated. I’m guessing your end result has been a milky, grayish effect. If you want to get those vibrant hot colors, I’d recommend using a low fire earthenware body and firing between cone 09 and 02. The glass I’d predict would work best would be either Spectrum (96 COE) or Bullseye (90 COE.) If you really wanted to go for broke and get some amazing results, you might want to play around with Boro dichroic glass- However, I’d make absolutely certain the dichroic coating was in the inside (facing the clay body) not the outside (otherwise it would probably just burn right off.)

    Again, this is all from the perspective of a glass artist and it’s all theory. I haven’t actually tried this yet. However, I can’t wait to see what actually happens when I do!

  • Casey C.

    Hi to Steve! Love this technique – Funny we were just talking about glass + raku at the studio the other night – one of our regulars was interested in trying it. Glad we had the workshop under our belts to discuss the methods with her. Such fun, hope we can do another some time. Cheers!

  • Steven B.

    Thank you all for your comments and your very kind words about my worK. I’ll try to answer your questions:

    Francine: I bisque to cone 08. My raku firings are approx the same though I fire by visual observation, never using cones or pyrometer.

    Heidi: I use flat colored glass so I have no direct experience with bottle glass. Go ahead an experiment but protect your shelf and other pots from melting glass that might drip.

    Velda: Petuntze is generally accepted as a substitute for Corn Stone though it is not quite the same.

    I’m happy to answer questions. Please feel free to email me directly at sbranfpots@aol.com

    Steven

  • Leslie G.

    Steven,

    I have also thought about adding glass windows in ceramics but I haven’t tried it. In theory though, I’m thinking that if one were to take completed ware and then fuse/slump glass, it should work. Haven’t wrapped my head around how to pull this off unless it was on a platter, plate or some flat design.

    I guess if I wanted to add glass inside a piece of ceramic vessel, I’d take the finished piece (unglazed on the inside), heat it to the same temp as the soft working temp of my glass, and blow a glass vessel from inside. It seems like the inner glass vessel would not only act as an inner glaze, but depending on how much I worked the glass, it might even puff out where the cutouts in the ceramic ware are.

    However, there’s also the possibility that if there are a lot of air bubbles between the two vessels, the piece might explode during the glass annealing stage.

    I’d be very eager to see what this would look like and it might be really interesting if you wanted to pursue this and collaborate with a glassblower to see if this would actually work.

    Leslie Griffin
    Gainesville, FL

  • Steven B.

    Leslie,,,,,,,When I first began my experiments with glass and clay, glass “windows” was how I saw the collaboration of the two materials! The approach I took was to cut out sections of the wall of my vessel and the after glaze firing use the copper foil/stained glass method. I would cut the glass to fit the cutout, wrap the edge of the cutout with copper foil, wrap the edge of the glass, insert the glass and solder the foil.

    Good luck with your experiments. Keep me posted directly sbranfpots@aol.com.

  • Darlene M.

    I fired glass in bisque and to cone 10 but expect lots of crackling and running like water at cone 10 temps.
    Glasses melt at different temps so if you buy at an artists shop you can ask, but color and other factors can change even the general rules for a COE rating. Glass like pyrex tempered for cookware or lab equipment typically has a higher melt temp. Found glass or craft glass pebbles is anyone’s guess.

    Some general melt ranges are found here- http://hypertextbook.com/facts/2002/SaiLee.shtml

  • glass is silica
    silica is in clay and glaze
    silica can be heated to may different temps and is probably the most versatile property in the above mentioned
    silica is found in nature as sand and/or quartz
    its also often found as a blend:)

  • I’ve used small (.25 to .75 inch sizes) colored pieces of glass on a wide shouldered vessel with a clear crackle glaze underneath, fired to around 1875 F. Raku.

    I made a channel for the pieces to sit in on the shoulder that was horizontal, then as the glass melted, it mixed beautifully with the glaze, and ran part way down the sides of the vessel. Didn’t have a problem with it sticking to the kiln shelf. Used a single row of pieces of glass, not a thick layer.

  • As a glassblower, I have noticed that the cool colors are not as stiff as the warmer colors. Try using blue glasses for cooler firing temps and the reds and oranges for the higher cones. I will be trying my glassblowing colors in my pottery to see what happens. Never thought of it before… good article.

  • Nancy W.

    THIS IS EXACTLY WHAT I HAVE BEEN LAYING AWAKE ENVISIONING….ALSO…WHAT ABOUT APPLYING GLASS CRUMBS DIRECTLY TO A RED HOT SURFACE…ALSO POSSIBLY COPPER FILINGS OR GOLD LEAF…WHAT WOULD YOU PREDICT WOULD BE LIKELY TO HAPPEN

Enter Your Log In Credentials
This setting should only be used on your home or work computer.

Larger version of the image

Send this to a friend