What the thread establishes
The answer.
Nikawa-urushi is one of three principal urushi-based adhesives, distinguished by the use of animal glue (typically hide glue) rather than a starch. The glue is hydrated and gently heated to a syrupy consistency, then mixed at a ratio of one part glue to four parts raw lacquer, producing a very thick, stringy adhesive. It is applied and the parts joined in the same manner as mugi-urushi. The assembled piece is left to cure at ambient conditions for roughly three days, at which point squeeze-out is scraped away and alignment is checked; the piece is then moved into a humidity-controlled curing room. Because the adhesive cures slowly and the surface can seal over before the core has set, the practitioner waits at least ten days—ideally a month—before applying sabi putty. The longer cure time is the trade-off for the superior bond strength, which is useful on a teapot that will see repeated thermal cycling. Yixing clay, despite being unglazed, often has a waxy, non-porous surface that makes masking largely unnecessary and allows stray lacquer to be scraped off cleanly, though individual pieces vary in porosity and should be tested.
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What goes wrongThe primary failure mode noted is that nikawa-urushi cures quickly on its surface while the interior remains unset, effectively sealing in the uncured core. If the squeeze-out is not cleaned away after the initial ambient cure, the trapped material continues to cure slowly and the next step (sabi application) is delayed. In the thickest areas the adhesive can remain soft enough to be scraped off and reused on another piece even after three days.
What recovers itScrape away the squeeze-out after roughly three days of ambient curing. This removes the sealed surface layer, exposes the still-uncured core, and often accelerates the remaining cure enough to proceed to the next step after about ten days rather than a full month. Check alignment while the bond is still flexible; nikawa-urushi retains enough workability that parts can be repositioned even a week into the cure.