Stoneware or Porcelain? Learn to know your object
Possible Kintsugi mistakes
In the traditional practice of kintsugi, repaired objects are usually made from two types of materials: stoneware (called tsuchimono) or porcelain (called Ishimono). In the photo we can see that the cross-section of a stoneware piece has a porous and rough texture, which promotes excellent adhesion of the lacquer. In contrast, the cross-section of porcelain is characterized by its hardness, smooth surface, and low absorption. If we use the same method as for stoneware, this could result in a loss of strength increasing the risk of the object coming loose during use. In order to avoid this problem and improve the adhesion of the lacquer on porcelain, it is necessary to create roughness on the surface using a file or a mini-sander to make it rougher and facilitate adhesion. .
Sute-Urushi
Preliminary preparation
. Stoneware ceramics are easily stained by lacquer due to their porosity. Therefore, when raw ki-urushi lacquer is used in mixtures with a high water content such as mugi-urushi or nori-urushi, it can penetrate deep into the material by capillary action, causing a risk of brown spots around the surface. Your assembled part and your joints (illustration in the photo).
How to prevent this error?
It is essential to inspect the quality of your ceramics, especially those types of ceramics that may be affected by lacquer and would require treatment with the application of sute-urushi. This concerns in particular unglazed ceramics, those with partial enamel, as well as those of white color or light shades.
Sute urushi material
- Ki-urushi
- Small brush
- Turpentine
- Towel or rag
- Small plate
Protection and grip
Mix a small amount of raw ki-urushi lacquer in a bowl with the same amount of turpentine (50/50). Apply your sute urushi mixture with a small brush to any rough surfaces, then wipe them immediately with your tissue/rag. Wipe by pressing on it to remove the excess.
Drying
Several methods:
- Burning with a small candle. For 1 to 2 minutes, pass the piece over the flame covered with the sute-urushi mixture
- Place your piece in the oven at 120° for 1 to 2 hours
- Let your piece dry naturally in your Muro 24/48 hours (the best practice, although it takes a little longer)
In conclusion, this method will create a protective layer on the breaks, effectively preventing the migration by capillary action of excess humidity inside the room, while restoring the integrity of the edges preventing them from becoming brownish or blacken.
In addition, it will considerably improve adhesion for mugi-urushi/nori-urushi, reinforcing the strength and longevity of the bond. This technique is also particularly beneficial for protecting stoneware items from stains and improving adhesion for porcelain. Sute-Urushi Tutorial
Chijimi
The most annoying mistake that can occur when using Kuro Roiro lacquer is what in Japanese is called "Chijimi", which is characterized by the appearance of shrinkage, wrinkles or waves. .
It is rare to find a complete explanation of “Chijimi” in kintsugi reference works (in Japanese). Therefore, I will summarize the possible causes of this technical error.
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The phenomenon appears in kintsugi during the muro drying of kuro roiro lacquer. When lacquer is applied and dries, it is said to have shrunk. This “shrinkage” is comparable to wrinkles caused by paint. The layout in the muro can be one of the consequences of Chijimi and the lacquer can leak (see the Chijimi photo). The lacquer slides from the edge and creates a thickness that will wrinkle and shrink as it hardens. In this example, I placed the bowl in the muro on its base which created the chijimi. The ideal would have been for it to be placed horizontally or upside down on a base, while changing its position after a few hours during the lacquer hardens process.
Chijimi also tends to occur during drying when the humidity is too high.
How to fix Chijimi?
Do not attempt to correct until the kuro roiro is completely dry and hard.
- You can use a small kanetsu knife (very sharp) to delicately level the top, finishing it with #800, #2000 waterproof sandpaper.
- I make the correction by sanding using waterproof sandpaper with grain size #800 and #2000, adding a little water. You will notice that the correction is not easy due to the difficulty in eliminating imperfections, especially "Chijimi". The correction concludes with the application of a new layer of lacquer as thin as possible to obtain a perfectly smooth surface.
Precautions to avoid shrinkage
The following settings vary depending on the type of material you are painting and where you are doing it:
1 - The thickness or fluidity of your lacquer during its application
2 - Make sure there are no visible brush marks. Have you made the right choice of brush, its size, the length of the bristles?
3 - Observe if any areas require a thicker or thinner layer where "Chijimi" is likely to occur
4 - Adjusting the temperature and humidity in the Muro
For a slightly thick layer (personal experience) I tried a lower humidity level 55 to 60% with a temperature of 20 degrees Celsius or more. I avoided the "Chijimi" phenomenon, but the drying took longer. When I apply a very thin layer I place it in the muro with a humidity of around 75%.
Note that it is very difficult to find the ideal heat and humidity level, each case requiring a different approach.
The mistakes are mainly based on my experience and failures.
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