I am working on this broken bowl. It is nice but was shattered. The final repair will have four major pieces although the photos show three. One had a hairline crack so I finished the break.
The next step is to start cleaning the same as before. You will repeat this process until you have the seams smooth. The steps that follow this cleaning in kintsugi won’t hide any irregularities you leave from this stage. That is, a smooth seam will finish smooth, a rough or not well matched seam will finish looking rough or not well matched. Take as much time as you can to go over and over the seam. The surface of the piece will determine what you use to clean up with at this point. This is a medium fire glaze. I am using a 2,000 grit wet/dry piece of sandpaper to gently rub away all the excess medium. After applying the sandpaper and working for about a minute I immediately use tissue to clean up the medium since it will dry into a hard film if you don’t. So, sandpaper and water, dry and clean, sandpaper and water, dry and clean.
Pay special attention to the areas where there is a corner or a curve. Any place where the seam goes up and over from the outside to the inside of the bowl, corners where you have fit two pieces together. Those types of areas are the easiest to not apply enough medium and either have a jagged edge or, in the case of a corner, an actual hole where water will leak. A jagged edge on the rim needs extra medium applied, a hole in the body will also need to be closed with medium. The photo shows the second application of infill after it has dried. If you are working in a studio that is unheated overnight you need to be sure that the piece is not going to freeze for the first night. The water in the tonoko can freeze although the shinurushi won’t.
The inside of this bowl is a spider web of cracks. The hardness of the body and glaze is such that it didn’t break cleanly, without any glaze chips. It has a lot of glaze chips and a couple of hairline cracks. The glaze chips could be gathered and put back into place but I have found it is easier to do infill work. The process of trying to hold small chips with tweezers and finding and placing them back into place takes me more time than filling the indent with medium and sanding it down. All of the seams in the photo that show white may need to have fill work done. The white is the body of the piece showing. A perfectly matched piece would show only the color of the glaze. Porcelain that is high fired will break in a clean fashion but lower fired pieces like this bowl don’t break as cleanly.
In the photo I have also applied medium to the lip of the bowl where there is a poor fit between the two pieces. Rims should receive special attention since the mouth is sensitive and touches them. I said mismatched seams should get narrow beads of medium before. On the rim I will change that to say give them a little extra. A seam that varies in width, i.e., one that goes from thin to a little thicker in width, doesn’t look bad if it is done well. In order to not have a sharp edge on the rim you should make the bead a little thicker. The way to tell if a seam needs infill is to run your finger along the seam, both lengthwise and across it. If you can feel a sharpness or a bump then it needs attention.
Secondary patching is easier than the first time around when you had to think about collapsing the piece. This time the piece should be, within reason, structurally sound. You need to apply the medium as precisely as possible as fits each different type of re-fill. If it is a mismatch of pieces you should apply a very little amount to the very tip of the knife and deposit it directly into the area you want it to be. Move the palette knife into the mismatch area, packing the medium in, and then withdraw it so you don’t loosen the medium. The neater and cleaner you do this will determine how much you will have to clean up after you have given it time to dry. Indented areas should be filled and using the knife as a leveling instrument, make the indented area as smooth as you can to the surrounding areas.
The tonoko is completely mixed when you have no more pockets of powder in it and it is a consistent texture throughout the whole mix. At that point add some shinurushi. A convenient way to measure out how much to use is to lay a bead the same length of your mixed tonoko. The shinurushi needs to be mixed in well, leaving no pockets that don’t have any mixed in. It is possible to add too much or to not add enough. If you err, too much is better, too little will leave a brittle medium that will fall out of the fills. After you get this secondary mix ready heap it into a pile on the glass to keep the edges from drying out. Clean the excess off the best you can from both knives and you are ready to proceed to applying it to the piece.
To use tonoko you should first put out the amount you want on the glass. Using a water dropper measure out a couple of drops of water and mix it in. I use two palette knives, one to mix, one to scrape the mixing knife. The difference between enough water and too much water is usually a couple of drops. If you get a mix that is runny and won’t absorb the excess water then you have too much water and need to add some tonoko. That is what happened with my mix in the photo. The bowl I am working on really only required a very little amount of medium but I added too much water and so had to add more tonoko powder. Be careful, it can get out of hand very easily. The consistency you want is a slightly soft mixture, not so hard that cracks appear when you mix, not so soft that there is excess water on the glass.
Both the inside and outside of this bowl have narrow seams, thick seams, and misaligned pieces. It requires all the different kinds of secondary work. Fine line fill, indent fill, and building a smooth transition between 2 pieces. For the infill work I am going to use tonoko instead of flour or rice. Flour and shinurushi mixed together has a strong body and is springy when being applied. If you put it into a narrow crack it tends to partially come back out with the palette knife. Rice would work OK but it takes a long time to mash-up and prepare. It has the disadvantage of being a little springy when applied. The springy nature makes it difficult to apply to narrow cracks. Tonoko has very little spring and is well suited for all the three types of work.
Narrow seams that don’t align well will need a special type of refill. Instead of adding filler to an indent to bring it back up to level you will need to add fill to the higher of the two sides in order to make a smooth transition to the lower piece. You need to add medium so that the transition between the two pieces is smooth to the touch, not an abrupt edge or a sharp edge. I also suggest to keep your ‘ramp’ seam as narrow as possible since that is going to be your seam you apply gold or other metal to. Shinurushi is different from polymer, epoxy, based adhesives in that it won’t give you a raised finished surface. It will finish as smooth as you like it to be. Because of this a narrow transition seam between mis-aligned pieces looks nicer and is easier to finish.