Seamless Transitions: How to Spray Layers of Glazes to Softly Blend Glaze Colors

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If you are a ceramics nerd and see a Martha Grover pot in person, you are likely to marvel at the glaze surface and try to guess at how she came up with it.

In this post, Martha Grover explains that her surfaces, which are often mistaken for soda-fired surfaces, are actually achieved through spraying on various cone 10 glazes. – Jennifer Poellot Harnetty, editor.

 


 

Glaze detail on finished pieceI started spraying my glazes about 4 years ago. I found that I was unable to achieve evenly layered surfaces and color transitions through traditional methods of dipping and pouring. By using two sprayers, one small for my bright colors concentrated at the edges, and a large one for the overall piece, I am able to create a varied, even surface that shifts from a bright color to light seamlessly.

To begin, I bisque my porcelain to cone 04. I find any lower makes my work far too fragile, while firing it hotter causes the piece not to take glaze well. Each piece is then waxed on the bottom and any other surface I wish to remain glaze free – in the case of the butter dish, I also wax the top slab of the lid.

Applying slip dots

Applying slip dots

I then pour glaze into the inside of each piece. I have tried spraying all layers on the interior, and find that is extremely difficult to fully cover any interior vertical surface, especially in bulbous forms. By pouring this first layer, usually with my Salt Yellow Base, I ensure that the interior will be completely glazed. Then I wipe off any excess that may have spilled over the edge.

Next I let the work sit and dry overnight – this is VERY important. If I try to glaze the exterior on the same day, the glaze will pull away from the surface due to over saturation and I end up with unglazed bubbles on the finished work. The next day, I apply my brown dots with a fine tipped slip trailer. These are a high iron engobes, which can be put on either bisque or green ware.

 


Safety Notes!
Always spray in a well ventilated area or spray booth.
Be sure to wear a respirator.
I always wear latex gloves and ear protection as well.


 

Spraying clear layerThe next step is to dip any handles. Much like the interior of the pots, it is hard to get a full coating of glaze on the backside of a handle with the sprayer.

I then proceed to spray the whole piece using my large sprayer, a “Husky” siphon feed spray purchased at Home Depot. I first spray on my clear layer. I make sure to spray up under any folded edges. I make this layer thicker at the top edge and fade out as I get to the foot of the pot. Once again, I wipe off any overspray that may cause dripping in the next layer.

I change over now to my opaque glaze. For this, I use my Salt Yellow Base, with whichever colorant I need to achieve the desired color; on this butter dish it is just the base alone. This layer I spray heavier at the bottom and lighter at the top edge. This varied layering is what causes the snowy affect in the glaze where the two cross over one another.

The final step is to once again wipe off any over spray. In places where it is difficult to clean with a sponge, I use a metal tool to scrape off excess glaze and then a damp sponge to clean off any remaining residue.

The finished piece is fired then to cone 11 oxidation in an electric kiln. I always sand the exposed porcelain after the final firing to create a smooth silky surface.

 

Click to enlarge images!

Click to enlarge images!

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To learn more about Martha Grover or see more images of her work, please visit http://www.marthahgrover.com/


**First published in December 2013
Comments
  • Nancy Z.

    I enjoyed this article….have been wanting to try spraying for some time on my raised leaf platters to clarify the leaves. Sometimes they are lost when the dipped glaze is a bit too thick! Thanks for the info and the glaze recipes!

  • Joanne S.

    Beautiful work – and interesting to learn that a lower firing of the bisque can help with the glaze adhering.

  • Vanessa L.

    Hello Martha, I have wanted to spray graze for sometime, but had no clue how to begin. You explained it so throughly that I feel confident I can do it and like the results. I appreciate you and all the other professionals who share their successes with everyone, you rock! Be blessed today and always.

  • Larry K.

    I use a number of glazes that are layered and sprayed around each other. To do this I use up to 16 HVLP spray guns (the $45 ones from Harbor Freight). When I began spraying all the things I disliked about glazing disappeared and my forms came to life.

    So many potters are afraid of spraying and many hate the noise of the compressor. Put the compressor out on the back porch or in a closet (thats where mine lives) to cut down on noise. There are many potters using shower enclosures as spray booths. The plans for these can be found online.

    Spraying is not hard.

    Martha’s work is wonderfully simple, complex, understated, and much, much more, all at the same time. Like really fantastic comfort food, you just want more.

    A short look around her website will show just how she has mastered her forms and glazes. A unified body of work. This is my shortcoming, but I’m working on it.

    Thank you for sharing with us Martha.

    Larry Kruzan
    Lost Creek Pottery
    http://www.lostcreekpottery.com

  • Robert B.

    I saw this post and wanted to see someone else spray glazes, too. I’ve been spraying for years to create a gradation of different colors. I use an external mix spray gun for all of my pieces, which are fired to cone 3 electric. for those who want to see my work, and examples of my spraying, go to http://www.BobBrehmerPottery.com. Martha’s work is very nice and has a softness to it.

  • Your gun appears to be a Chinese knock-off of the old Binks Model 15. I have the original, and still use it. These are not HVLP guns; they were made for lacquer touch-up work. Better replacement parts for these guns, made by Binks, can still be found at auto body supply stores and professional paint vendors.
    Since glazes are “let down” with water instead of a solvent, I recommend getting a stainless needle and matching air-cap for greater longevity. Make sure the needle packing nut is kept lubricated, and just tight enough not to suck in air. 25 or 30 p.s.i. of air should work with all but the thickest glazes, so you all need regulators too.

    • Can you advise what you feel would be the appropriate level of extraction for the spray booth with this type of spray?

  • Martha G.

    A few additonal notes on types of sprayers.

    My Husky is a “Detail Spray Gun” with siphon delivery. I cant find a
    model number on the box but its sku is 515-547. I find that I have a
    lot less over spray and much more control than when I have tried an
    “EZ sprayer” or other type sold at ceramic supply stores. The one I
    use has the capability to change the amount of air that is mixed with
    the glaze as well as the amount of glaze that comes out.

    My small detail gun is a Badger 250. It is the simplest and cheapest
    model that they make. It is very easy to clean if you get a clog and
    I find I am able to cover a fairly small area with it. Here is a link
    to their site: http://www.badgerairbrush.com/BADGER_250.asp This is
    my favorite of the types I have tried. The other fancier models I
    have found clog very easily with glaze and are a pain to clean,
    requiring you to tear the entire gun apart to clear a clog.

  • Hi Martha — very nice work. I like the attention to detail; those little things like wiping off the overspray and sanding the exposed clay after firing are the marks of a true professional. I use a Critter sprayer, purchased at Lee Valley Tools. Like yours, it can be adjusted at the nozzle to control the spray pattern. It’s also very easy to clean on the rare occasions that it gets clogged. It is a real workhorse. Thanks for the tip about the Badger airbrush. I’ve been looking for a low-cost and effective airbrush and will take your advice.

    Michael Giles
    Victoria, BC

  • Hi Martha. It’s me, Claire from Northern Clay Center. So good to see your work is getting its much deserved recognition. I noted that you are sanding your exposed clay after firing to ensure a nice smooth surface. I wonder if you have ever considered applying terra sig (applied on greenware) made from your clay body to that surface. At cone 10/11 there won’t be much (if any) sheen. But the surface will be very smooth and inviting touch. Terra sig on surface where lid parts come together also makes a nice contact zone.
    Anyway, still admiring your work and as usual, appreciating your generosity.

  • Julie B.

    can anyone recommend a compressor than is smaller size and less expensive that will give enough pressure to spray glazes? beautiful work Martha.
    thanks.

  • Debora R.

    In the past I have used a sprayer but it was in school. Now that I have my own studio and a compressor I would like to know the consistency the glaze should be. My sprayer clogs easily and other than getting a new sprayer I think my glazes are too thick for the nozzle.
    Any input would be greatly appreciated.
    Love the look btw.
    Kinda Regards,

  • Subscriber T.

    Hey Martha,
    It’s really great to see your work all over now! You have worked really hard to get where you are now! Hope you are enjoying China!

  • Subscriber T.

    In regards to using a sprayer I have been using a siphon fed HVLP sprayer I picked up at Harbor Freight for less than $20 here (http://www.harborfreight.com/heavy-duty-air-paint-spray-gun-97855.html).

    Those of you who are doing detail work you can also use an artists airbrush with a size 4 tip or larger. For these small airbrushes though, you will need to sieve your glaze with a 100 mesh sieve at least! If your glaze clogs either go with a finer mesh sieve or a larger tip size. Of course there are many considerations here but the best way is to practice on some test pieces. And play with it till your get what you like! Experiment, Experiment, Experiment!

  • Subscriber T.

    @julie – You need a compressor with at least 30-45 psi (your sprayer documentation should say what your specific model needs) I use a 5 gallon shop compressor. The larger the capacity the less often it has to start up and pressurize the tank. Bigger is better if you don’t like the noise or getting startled by the engine starting up at random intervals.

    @debora – I mix my glazes to a hydrometer reading of around 45-55. This is a good consistency for both dipping and spraying. But I also sieve my glazes with at least an 80 mesh sieve. But, my “look” has been built around that and all my glaze test are built on that number. If you are dipping your pots in a thicker glaze then you will need to also spray it on thicker to get the same look you want. Some glazes have materials that have a larger particle size(granular rutile, glass frit, etc) that may come out in the sieve so be careful. If there is a lot of granular material left in the sieve(over a gram or so in a small jar of glaze) then you are changing the material ratio and the glaze won’t come out as you are expecting. We have a few glazes that cannot be sprayed because the particle size is too big for the sprayer and the glaze comes out looking like junk if we sieve it. So just as a warning!

    Below are some links to a hydrometer and another way to make a cheapo one.
    Hydrometer – http://www.bigceramicstore.com/amaco-hydrometer.html

    Cheapo Hydrometer -http://ceramicartsdaily.org/clay-tools/making-clay-tools/how-to-make-a-floating-stick-hydrometer-for-the-cost-of-a-milkshake/

  • Dan H.

    When using a husky gravity sprayer, be sure to remove the small interior screen in the gun. It always gets clogged. A tip from Tom Coleman and Frank Massarella. Also and this is critical, when putting glaze in your gravity sprayer, use a small kitchen strainer while you pour your glaze into the receptacle. There are always bits of sponge, chunks of glaze and so on that will immediately clog the spray gun.

  • Maggie R.

    She didn’t use a lower firing of the bisque – Cone 04! Cone 04 is higher than the normal cone 05-cone06!
    Maggie

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