Slip Habit

All about slips and stains!

It took me a long time to start experimenting with slip in my ceramic practice, simply because there is so much to learn.  I didn’t have a very clear idea of what slip was anyway so I just ignored it until another member at the same community studio offered me to use a bucket of his porcelain slip to experiment with.

I dipped a red clay pot that was still moist in it and started carving the soft white surface of the slip so the red clay appeared underneath. It is the sgraffito technique (sgraffito comes from Italian, and means “to scratch”). I loved it.  

From then on I figured out how to make my own slip. It didn’t take long.  Clay + water.  That’s it. You might need to blend the slip to get rid of lumps.    Slip is just liquid clay.  You can adjust the amount of water to get the slip consistency you need.  Usually porcelain is preferred so you get a white slip, but some people also use wild clay as a slip to give interesting earthy colors and effects to a piece made with a sturdier clay.  Wild clay can be low fire, but if used as a slip, you get your cake and eat it too: you have a sturdy piece underneath and an interesting slip as a surface decoration.

Slip to stick and repair

Slip is also very useful to stick different pieces of clay together, for example a handle to a mug.  You can scratch the piece, add some slip and glue it together.  I add a little bit of white wine vinegar to my slip to make it stick better. I have also made paper slip to fill in cracks and repair broken pieces after bisque firing (yes, it works on bisque too!).  To make paper slip, you can just blend some slip with shredded toilet paper.  There are recipes online.

Colored slip/clay/glaze/wash

What I didn’t realize until much later is that you can also use stain to color your porcelain slip.

I first bought stains to make colored clay to do Nerikomi ceramics (more about this process here).  From then, I sometimes used the stain as a wash (stain+ water) especially to stamp letters on my pots.   But eventually, I figured out that all the colors I used to make colored clay could be used to make colored slip as well.  I know, duh…

I’m still mad at the time it took me. Once at my old community studio, someone asked me how they could cover their pot with a matte black surface, not a glaze. I recommended a wash with black stain, but she should have used black slip and I didn’t know enough at the time to give the right answer.

The inside of these pieces is painted with colored slip

“Propeller” Porcelain Cylinder. The wings are made with a Nerikomi pattern. I make my own colored clay by mixing porcelain with stains, then use different colors of the same clay to create the pattern.

Ceramic “Paper” boats with imprinted words (stamped with a wash = stain+ water).

Making colored slip with stains

The last thing (that I know of) you can use stains for is in glazes.  I have a potter friend who makes a clear glaze and just adds stains to her glaze to create different colors.  Personally, I just paint with my colored slip  (or use my colored clay to create a pattern) and then put a clear glaze over it.

Slip, clay, glaze, wash: Stains can be used in all of them.

But what are stains exactly?

Stains are manufactured pigments (the main company in the US is Mason Stains, but you can also find cheaper ones online at US pigments).

Oxides, on the other hand, are natural pigments (like copper oxide, iron oxide, copper carbonate (carbonates are not chemically oxides but are used in very similar ways in ceramic), manganese oxide, cobalt oxide, etc…). They work to color clays and glazes and slips (indeed, for a very long time, that’s the only way potters knew how to color their glazes, slips and clay) but they’re less stable and might not be food safe (= they might leach some harmful chemicals into your food that you will then ingest; the same reason why lead can be dangerous in ceramics), whereas stains are supposed to be stable.   Mason stains are “encapsulated”, which I don’t really understand but means it should not be toxic and shouldn’t leach when normal oxides might.  Here’s how one site puts it: “These lead-free ceramic stains are fritted raw materials. Frit is essentially one or more colorants encased in glass then powdered. This makes the colorants such as oxides and carbonates insoluble to your body hence much safer to use. All Mason Stains are also lead-free.”

One of the draw of oxides versus stains is that they give more natural earthy colors, because they actually are natural and mined directly from the ground.   But if like me you love bright colors then stains are your friends.

Once you have your stains and your slip, you can mix them together and have a huge palette of colors to decorate your pots. The ratio is 3 to 10% of powdered stain (lighter colors need more stain) to whatever amount of dry material you are using. For example, take 100g of dry clay that you will use for your slip. Measure 10g of Manganese pink stain or 5g of best black stain (for example) and mix both ingredients (clay and stain) with water. When the clay dissolved, blend your slip until smooth. It sounds like a food recipe, just don’t eat it! Some of them have such beautiful colors they look like candy smoothie!

Note: Once you’ve made your slip, you can put it on a plaster bat and let it dry until you have colored clay.

The difference between colored slip, underglazes and engobes

I wrote that colored slips give you “a huge palette of colors to decorate your pots”. Does that remind you of anything?  Yes, underglazes!  Underglazes are just glorified colored slip.  If you have powdered stains and clay, you can make your own underglazes on demand.

Another word sometimes used for slip is engobe. Engobes might specifically refer to a slip that will vitrify on your pot when you fire it . The clay that makes up the slip will reach the vitrification stage and silica in the clay will turn to glass. But the two words often seem to be used interchangeably.

 About Sodium Silicate

 Once I started making my own colored slip, I found out that it would dry out fairly quickly. I had to keep adding water and mixing anew with a blender to get a smoother result. It took time and created a mess and more stuff to clean. I found out that if you add a drop or two of sodium silicate in your slip it won’t coagulate as much.  Ready for some vocabulary?  Sodium silicate is a deflocculant. It means that it disperses clay particles and prevents them from coagulating together.    A similar product is called Darvan (but I’ve never used it).   I still have some slips which dry faster than others, not exactly sure why (probably the type of material used to make the different colors in the pigment) and it can take time to get them back into a smooth slip texture. Underglazes can be less work, since they’re ready to use, but I bet you making your own slip is a lot cheaper (although buying stains and oxides is still expensive) and once you have stains and clay in your studio, you don’t need to go to the store and can just manufacture what you need.

Slipcasting and other ceramic techniques using slip

Sodium silicate is an ingredient used in casting slips.  Slipcasting is a technique using slip to create ceramic pieces from plaster molds.  Another thing I’ve never tried, even though I really want to layer slips of different colors and then carve through them.  I’ve seen beautiful work made this way (see Forest Ceramic Co work in the United Sates).   I even made a plaster mold for this, so I need to try it.  So many techniques, so little time!

There are plenty of techniques I’ve tried with slips though.  Sgraffito, as I mentioned.  Inlays, which is the opposite of sgraffito: you carve a pot, cover the carved area with slip and when your piece is leather hard, you use a metal rib to scrape off the extra slip, and the only color left will be the one stuck in the carved area.  It looks great!

Inlaid piece

Sgraffito piece: it was covered with a grey slip while leather hard, then the words of a French poem written on it.

I’ve tried making bubble slip.  I used to do this with glazes, and I figured it could work with slip and I tried it.  Add detergent to your slip, add water if too thick, and blow with a straw in a narrow glass.  The bubble will raise over the top of the glass and fall on your piece.  Just be careful not to breathe IN the straw.  You don’t want to drink slip.   The other thing to be aware of is that because slip is clay, there is actually texture on the pot once it dries.  The outline of the bubbles won’t be smooth.  It can be a good or a bad thing depending on what you like.

I have let drips of colored slip fall on my pots, either while the pot is turning around, or motionless. Here as well, there is texture.

masking tape was put on this egg over three different layers of colored slip to create this pattern.

Drips bowl

Bubble Slip decoration

I have stuck stencils to a pot (you can use wet newspaper cut into the shape you want and stick it to greenware pot), covered it with slip and then peeled off the stencil. You can have several layers of slip one over the other and add stencilsafter each layer so all colors will be visible when you peel off the stencils. You can make quite intricate designs with this technique (see Georgie Gardiner’s work for much better examples). If you use a sticky tape to mask some areas of your pots , usually on a bisqued pot, the technique is called mask resist. It’s normally used with glaze to create sharp lines on a pot, but you can use slip. I have seen people use rubber bands as well to mask areas of their pots. Anything you can think of is worth a try!

I once took a paper clay class where we dipped all sorts of organic stuff in paper slip: wood sticks, leaves, cotton doilies,  anything. You want organic material so that when it burns off, you don’t breathe in some nasty fumes. I even tried to use a pipe cleaner (it broke during firing…). Once fired, the organic product would burn off and you would be left with the clay imprint of the object. It’s fragile even though paper slip is stronger than normal slip, but you can dip something into slip and then apply it on the surface of a pot to create a texture. In this case, it’s not as important if you use normal slip instead of paper slip. And you can use colored slip. My next project is to dip wool yarn in slip, stick it to a pot and see what happens.

Chips of dried slip scattered on a white slab and rolled out

egg covered with yarn dipped in colored slip

Net-like fabric dipped in colored slip and applied to the surface of a pot

Another technique is to brush colored slip on a piece of newspaper or cling plastic and let it dry. Once dry, you collect chips of colored slips and you can layer them on a slab and roll them our with moisture (cover your slab with a wet piece of cloth) so they get into the clay. I love the effect!

Another thing you can do with slip is mocha diffusion: You coat a piece with white wet slip, and before it dries, you let a drop of nail polish remover mixed with stain fall on your pot from a brush.  The stain/polish remover will spread on the slip like capillary vessels.  Unfortunately it doesn’t seem to work the other way round (dip your pot in colored slip and use drip plain nail polish remover on the pot),

You can also try slip trailing.  You put slip in a small container with a narrow opening (like a syringe) and drip the slip dot by dot on your pot, or create a fine line to draw a design.  It takes a little bit more patience than I have, because your narrow opening will get clogged fairly regularly, but I’ve seen beautiful work done with this technique.

You can also squirt some colored slip onto a plastic cling wrap that is crinkled, let it dry some then apply it onto a slab (or a 3Dpiece, but it works better on a flat surface). Roll over it and you will get interesting pattern from the lines of the cling wrap digging into the clay and creating interesting effect.

I also tried creating a bowl over a balloon “mold” with paper slip. Blow the balloon but not too much, or it will explode from the pressure. Put painter’s tape (the blue kind that you put around windows when you paint so you have a clear line) around the balloon so the clay doesn’t stick to the plastic. Then put slip around the top half of the balloon to create a bowl shape with slip and let it dry. I used a cake piping bag from the dollar store to spread the slip. I used paper slip, but it was fragile and broke when I tried to transfer it to a mold while it was drying. I have not yet succeeded with this technique but that’s something I want to try again with colored slips. I think it could create amazingly thin pieces with interesting texture… if it works. I never said ceramics was easy….

Simple Slip Trailing Vase

cling wrap with drips of colored slip was used to create the pattern on this bowl

Mocha Diffusion technique was used on this egg

I have found another advantage to colored slip that only applies if you also do Nerikomi.  Because I make colored clay with stains, I can create the same color in slip and use it for example to cover a crack on a Nerikomi piece and the color of the slip will match the color of the clay.

So if you haven’t started experimenting with slip and colored slip, you definitely should.  It’s great fun. Let me know if you have other techniques I didn’t mention.

Caution: any time you use stains in their powder form, you should wear a mask.  You definitely don’t want to breeze the stuff.  That also applies when you’re scraping the slip from your piece if you made an inlaid piece.  And if you have cuts or sores on your hands, you probably should wear gloves when touching the liquid slip.