If you’ve come over from NCECA Minneapolis, welcome! In this post I’ll be detailing my process of testing nine commercial bisque-mend compounds. This will be a lengthy post describing all nine materials and their performance though each step of testing, with pictures. If you want to skip over the test process and get straight to the results, head to this post.

Before I begin I need to thank my partner in this testing venture, TJ Erdahl. He contacted the manufacturers of these compounds, who were all generous enough to send me free product for this testing project. Naturally, I also want to thank Amaco, Archie Bray, Apt II, Marx, The Ceramic Shop in Philadelphia, Duncan, and Spectrum for sending me their products. Clicking on the links above will take you to the product page for materials I tested. I will also post product links later in this post, since both Marx and The Ceramic Shop sent two mending products.

I set up my test to cover five things: filling a crack at the green stage, re-attachment of breakage at the green stage, filling a crack at the bisque stage, re-attachment of breakage at the bisque stage, and how the product looked when covered with a black underglaze that I use in my work. I did not apply glaze over any of these tests. I bisqued all products to cone 06, and glaze fired to cone 6, with the exception of Duncan, a low fire product. It was fired to cone 04. All firings were done in a Skutt electric kiln using the “slow” speed setting. All tests were done using a homemade white stoneware clay with a 14% shrink rate. If you plan to use any of these products, I recommend doing your own testing to see how the product responds to your clay body, glazes, and firing schedule. I hope you can use my test efforts as a springboard to help decide if any of these products can benefit your own studio practice. 

In order to test all of the factors I listed above, I made small sea lion figures which I purposely constructed poorly (a very odd feeling!), in order to encourage cracking and breakage. Each sea lion was cut in half and shoddily re-joined, to make sure there would be a crack to fill on each side. Each sea lion’s tail fins were poorly attached with minimal slipping and scoring, so that I could break them off and reattach them with the various products I tested. Once these forms became bone dry, I began the destruction and attempted re-construction. 









The base sea lion test form. You can see the crack already visible on the side, and the tail fins which will be broken off later.

To break fins in the greenware stage, I simply snapped them off by hand. After the bisque, I used a hammer and chisel. 

IMPORTANT NOTE ON PRODUCT SAFETY: You will see in my documentation that I sanded some of these products during my tests. If you choose to sand any of these bisque mend products, it is crucial to wear a particulate respirator and goggles, and work in a well-ventilated area, or outside, away from other people. I don’t believe a simple paper mask is sufficient for sanding these materials, as they release irritating and potentially dangerous particles when sanded. The Amaco product specifically comes with a caution label (CL), and a cancer and lung damage warning because it contains respirable ceramic fibers. The Bray product warns off sanding it at all, though their shop tech told me it is okay as long as you wear a respirator. I personally wore a cartridge respirator for every product on this list if I was sanding, and tried to keep sanding to a bare minimum. On this same note, I’m not sure I would recommend some of these products for use in the classroom, particularly at the K12 level, because of these safety concerns. Ironically student work is often where we need mending the most, but I also believe it is good to teach students about the properties of clay and how to work with them, without reaching for mending compounds automatically. If you want to use mending products in the classroom, I recommend choosing from some of the safer alternatives on this list, even if they are slightly less effective. 


Manufacturer: Amaco

Temperature: Δ04-10

Fired Color: Bright white 

Texture: Grainy paste

Notes: Can mix with stains or oxides to aid in color matching. Comes with cancer and lung damage warnings and Caution Label (CL) for containing respirable ceramic fibers. 


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I began by filling the crack with Amaco Bisque Fix using a plastic spatula. Then, I snapped off one of the tail fins and used the compound to re-attach it. Crack fill was very easy. Re-attach was harder, it is very fragile after mending. I had to do it twice because I accidentally snapped off my first mend. I found the mend more successful if I built up extra material around the re-attach to support it, instead of trying to limit the material to only being inside the crack. Sands down very smooth with sandpaper and a finishing sponge.

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Crack fill re-opened and a hairline crack is visible. Re-attachment looks smooth and strong, with slight discoloration around the mend area.


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Much easier to use than on greenware. Can be smoothed easily with fingertip, brush or sponge as it dries, lessening the need to sand. Holds re-attached parts together much more easily than in the green stage. Pleasant and easy to use in this stage.


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Crack mended in green stage has opened even further than before. Bisque-mended crack also re-opened and a hairline crack is visible. Both re-attachments look smooth and strong. 

BOTTOM LINE: Overall seems better for re-attachment than crack filling, and is easier to use on bisque. In fairness, bisque mending is what it is designed to do, and how it is marketed. I got better results when I built up some extra material around the mend and then sanded it smooth.  


Manufacturer: Apt II

Temperature: “High Fire”

Fired Color: Mixes with your clay slip, so that it matches the clay color

Texture: Milky clear liquid. Is labeled “Acrylic emulsion additive. Food safe and non toxic. Keep out of reach of children, do not take internally.” 

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When mixed with slip, makes a smooth material that is easy to use. As the product recommends, only mix this material with your slip, do not add extra water or the crack will re-appear as it dries. Can use fingers, rubber tool, or sandpaper to smooth. I found it easiest to apply with a brush, then smooth over the mend area with more slip on the brush and smooth it with a rubber tool when it approaches leather hard. 


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Crack fill re-opened and a hairline crack is visible. Re-attachment looks smooth and strong. 


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In their instructions, APT II recommends calcining slip made with APT II by firing a pencil of it to cone 018. Then, you are to crush that pencil into dust and mix with more APT II for mending bisque. This did work okay for filling cracks. No matter what I tried however, I could not get this method to work for re-attaching broken pieces. It is like trying to glue bisque together with wet sand. Ultimately, I resorted to re-attaching the broken pieces with Apt II mixed with green slip instead. 


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The green-mended crack has opened even further. The bisque mended crack shows as a hairline crack but did not re-open. I accidentally broke the green re-attachment fin when snapping off the bisque fin, so they both ended up getting bisque mended. Both bisque re-attachments did not pass the “wiggle” test, and broke off easily after the firing. 

BOTTOM LINE: Much easier to use on greenware, hard to use and not great results for bisque mending. Seems more like a slip thickener than anything. I found it most useful for repairing broken greenware as a Magic Water alternative. It did not seem very effective at helping to fill cracks.


Manufacturer: Archie Bray

Temperature: Δ04-10

Fired Color: Bright white

Texture: Grainy paste

Notes: Can be mixed with slip to help color match. I tried a 1:2 slip to patch ratio, but that still yielded a very bright white fired result. Comes with warnings against sanding or grinding, although the clay business tech told me sanding with proper ventilation and a respirator is okay. Cannot freeze or it is ruined. Bray usually will not ship this product between October and April because of that.   


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It was easy to build smooth layers of this for crack filling and re-attachment. On greenware, any product sitting on top of clay seems to have trouble adhering to it. When you smooth or sand it, any product outside of the crack pops off and falls away easily. This makes green re-attachments fragile. 


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Crack patch mostly worked, but a small hairline crack re-appeared. Re-attachment, however, did not pass “wiggle” test after bisque and fell off easily. 


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I tried adding some calcined clay dust to one of the bisque re-attachments for color matching. It sped up the drying time of material significantly, and seemed to still fire pretty white compared to the clay. Not sure this is worth it: it would probably be easier simply to try covering a Bray Patch mend with underglaze or glaze. Meanwhile, bisque mending with the material on its own is easy and effective. Easy to smooth with a sponge or finger to cut down on the need to sand. 


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The green mended crack has an odd result: it seems like the Bray Patch shrinks so little that the clay actually shrunk around it, causing the mend to partially squeeze out from the crack and detach from it. Meanwhile, bisque mended crack worked the best of any material. The crack is visible only as a slight depression, and did not become a hairline crack or re-open. Bisque re-attachments look smooth and strong. 

BOTTOM LINE: This was my favorite material out of the group, as it was easy to use, stayed smooth and solid, and did not allow hairline cracks to reappear after the glaze firing. However it does seem to give better results when used at the bisque stage. It is not good for repairing greenware. Because it shrinks so little, filling green cracks with it will actually cause more problems later on as the clay shrinks through two firings.


Manufacturer: Marx

Temperature: up to Δ10

Fired Color: Mixes with slip, so it matches your clay color

Texture: Peachy gel


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Makes a fluffy, “whipped” texture when mixed with slip. As it dries, it shrinks into the crack or mend line and several layers need to be applied.


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Crack patch shows reappearance of hairline crack. Re-attachment seems smooth and strong. 


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While snapping off the fin to re-attach, I accidentally snapped off the other fin and also broke the center seam apart completely. I used the mender to repair all three of these areas. Material behaved similarly as when repairing greenware, shrinking into the crack line as it dried and needing multiple coats. 


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While all of the mends technically held together, the mending compound blistered and lifted away from the piece in a truly unsightly result. 

BOTTOM LINE: I didn’t have a lot of luck with this material, except possibly as an aid when mending cleanly broken greenware. Doesn’t seem very effective as a bisque mend. 


Manufacturer: Duncan

Temperature: Δ04

Fired Color: Ivory

Texture: Silky slip 

Notes: The only low-fire product I tested, this was bisqued to Δ06 with the other tests, then glaze fired on its own to Δ04. Labeled “non-toxic.”


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Frustrating to use on greenware as it dries extremely slowly, and as it dries, it shrinks repeatedly into the crack or mend line. I found myself having to apply many coats and wait for a long time in between for each coat to dry. I was able to test three other products in the time it took to wait and reapply sufficient coats of this one. Even then, a hairline crack kept stubbornly re-appearing after the material dried.  


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Sure enough, a harline crack was visible where I filled a crack in the green stage. The greenware mend, however, stayed smooth and strong with minimal crack re-appearance. 


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I accidentally broke the green-repaired fin while snapping off the bisque fin. (This by now had emerged as unfortunate pattern, and a flaw in my test design plan to have these two repair areas so close together.) Once again, the product took forever to dry and repeatedly shrunk into the crack or mend line, necessitating many coats of the material. Once enough of it is applied, it is easy to smooth. 


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Green mended crack still shows a hairline crack, but did not get much worse. However this may be due to the fact that this is a lo-fire product. It was glaze fired only to cone 04, not cone 6 like the other tests, so it did not go through much more shrinkage from the 06 bisque. Bisque mended crack shows only a small hairline crack re-emerged. Re-attachments seem strong, however a small hairline crack does show.

BOTTOM LINE: The slow drying and high shrinkage of this product as it dried made it frustrating to use. I was able to re-attach pieces at both the green and bisque stages, but hairline cracks emerged along these mends. It didn’t perform well at all for filling cracks, which usually re-appeared as hairline cracks. This product may be best if used for small, clean breaks and then covered with opaque glazes. 


Manufacturer: Marx

Temperature: Up to Δ03

Fired Color: Ivory

Texture: Silky slip

Notes: Technically, this is another low fire product. It is the low fire counterpart to Aztec Hi-Fire Mender, also made by Marx. However that information was very hard to find. It is not listed on Marx’ website, nor on the product labeling itself, nor could the staff at Marx tell me this information. I ultimately found the firing temp on Sheffield Pottery’s product page for this product. By then, it was too late and I had already glaze fired this to Δ6. Comes with this warning: “Skin and eye irritant. Harmful or fatal if swallowed.” 


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Comes as a runnier liquid than most of the other mending products. Because of this, I found it necessary to build up many layers when filling cracks, as it shrinks into the crack or mend line as it dries. When it approaches leather hard, it is easy to smooth with a rubber tool. 


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Crack fill shows reappearance of hairline crack. Re-attachment seems smooth and strong. 


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Same behavior as when used on greenware: runny material shrinks into the seam line as it dries, necessitating several coats.  


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Green mended crack opened up quite a bit. Both the bisque mended crack and the bisque mended re-attachment show hairline cracks along the seam line. 

BOTTOM LINE: Another material I didn’t have much success with. It seems most effective in helping repair cleanly broken greenware. As a bisque mend, it allowed too many cracks to appear. However, I did technically over-fire this in the glaze kiln, so it may be more effective at its proper temperature range. 


Manufacturer: The Ceramic Shop in Philadelphia

Temperature: “High Fire”

Fired Color: Off-white, surrounded by a tan “halo”

Texture: Grainy paste with slippery texture

Notes: This product comes in white, buff, and brown to help match your clay body. I used white for this test. It arrived separated and somewhat dry, so I reconstituted it with a little bit of water and lots of stirring. The manufacturer recommends re-firing your piece to bisque temperature after applying to bisque ware, for better sanding results and glaze adhesion. Comes with this warning label: “May cause slight irritation to individuals with sensitive skin. Wash hands with soap and water after use. This product contains a chemical known to the state of CA to cause cancer. When sanding clay always use a dust mask. Do not ingest, keep away from small children.” 


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This material has a texture like wet sand, but with a slippery quality like sodium silicate. It dries fast so you must work quickly. Filling cracks with it is fairly easy, you pack it into the crack tightly with a rubber tool or plastic spatula. In fact, it is designed and marketed specifically as a crack fill, not a reattachment product. For the purposes of this test, I tried it anyway and sure enough, it was extremely difficult to use for reattaching broken greenware. It was like trying to use wet sand as glue.  Once it dried, it was also hard to smooth down using any means. Pieces would simply fall off and the reattached pieces would come apart again. 


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Crack is filled with little to no reappearance. Re-attachment held, but is very messy due to the difficulty of smoothing this product down without breaking the re-attachment.


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This was much easier to use on bisque than on greenware. Once again, filling cracks with this product was simple and easy. For re-attachment, I found that adding some water to the material seemed to help pieces stick together better. The manufacturer recommends re-bisquing your piece after applying this product to it, for better sanding results and glaze adhesion. I skipped this step, but it may be something wise to consider. When raw, the slippery, sodium silicate-like properties of this material will probably resist glaze or other surface treatments. 


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A similar odd result happened to the greenware patched crack as with the Bray Patch: the crack seems to have shrunk more than this mend material, causing the material to buckle and squeeze out from the mend line. The bisque patched crack seems decently closed, although a fine hairline crack is still visible. However, this may have been mitigated by re-bisquing the piece, which the manufacturer recommends but I skipped. Green re-attachment is messy due to the fact that I couldn’t clean it up very well. Bisque re-attachment looks better than expected, with minimal hairline cracks reappearing. 

BOTTOM LINE: I’d say this product has one very specific use: filling bisque cracks. It is easy to use and effective for that purpose. It can be used for bisque re-attachments, but it is challenging and inconsistent, and it was not good at all for mending greenware. In fairness, this product is marketed as a bisque crack filler, and that it does very well. 


Manufacturer: The Ceramics Shop in Philadelphia

Temperature: Δ04-10

Fired Color: Resembles a clear, heavily crazed glaze surrounded by an orange “halo” 

Texture: Sticky, slippery liquid

Notes: Texture is very slippery, like sodium silicate. I suspect it is an ingredient in this product.  


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It comes in a squeeze bottle and must be used like superglue: squeezing a bead along the mend line and pressing the pieces together. As a crack fill, it was completely useless- but in fairness, it is not designed for that purpose. This is marketed as a reattachment product. However, even for its intended use, I found this frustrating and difficult to use. The slippery, liquidy product runs everywhere and is super sticky and difficult to clean off. Excess material dries in a flaky, brittle layer like shellac that is hard to remove. 


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Crack fill revealed a crispy, flaky mess. Reattachment completely failed “wiggle” test and broke apart easily. 


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While snapping off the fin for the bisque mend test, I accidentally broke the entire piece in half. So, I used this product to reattach all three instances of breakage. It works much better in instances of perfect breaks: if holes or small shards are missing, it cannot fill them. Once again this product was messy and frustrating to apply, running everywhere and sticking to everything it touched.  


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Not a single mend worked. This piece came out of the glaze kiln in four separate pieces, with a shiny, crazed glaze-like surface everywhere the product was applied. 

BOTTOM LINE: My least favorite product on this list. It was messy, frustrating to use, and didn’t work on even one of my test mends. 


Manufacturer: Spectrum

Temperature: Δ04-6

Fired Color: White

Texture: Silky slip

Notes: On the manufacturer’s website, it says this product “does not develop strength until after it is fired.” Is labeled “Lead free, non toxic, dinnerware safe.” 


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Runny but very smooth. It is easy to apply, and as it approaches leather hard, it can be smoothed with a rubber tool or sanded down when dry. 


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A very fine hairline crack reappeared in the crack fill. Reattachment stayed together and seems smooth and strong. 


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When I took this piece out of the bisque kiln, a hairline crack had appeared around the entire midsection of the piece. Instead of breaking it open and mending the two halves, I decided to fill the crack with this material and see how it went. Re-attachments and crack fill went fairly smoothly on bisque. The product dries very firm without much shrinkage. When smoothing down this product, it is better to sand or scrape rather than sponging, which removes too much of this material too quickly. 


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I was surprised to find a fairly poor result in the glaze kiln, as this material was pleasant to use and had given promising results thus far. The hairline crack I had filled had  grown to split the piece almost fully in half, and the greenware re-attachment had completely disconnected. Since this material vitrifies slightly at cone 6, the piece that had come detached had then slid down and stuck itself back onto the piece with some of the vitrified mend material.  The bisque mend also showed the beginnings of separation. 

BOTTOM LINE: This material initially performed well when it came to re-attaching broken greenware. As a crack fill, it wasn’t as good. However, the good results in the lower temperature firings literally fell apart in the cone 6 kiln. This material may have better success at lower firing temperatures.  

CONCLUSION: Out of all these materials, I liked Bray Patch the best, and Mr. Mark’s Ware Repair the least. However, it is hard to make blanket comparisons between these materials, because many of them excelled at only one of the tests, while failing others. For example, Apt II was best for re-attaching greenware, while Mr. Mark’s Crack Pot was best at filling bisque cracks. Even Bray Patch, my favorite material, was ineffective at repairing greenware, or filling cracks at the green stage. For a concise wrap-up of all the results, check out this post. I might suggest picking the specific products from the list that suit your needs, and it may end up that you keep more than one on hand.  Happy mending!