Urushi-furo - how to cure urushi.

Locate and introduce the furo

The maker opens the video by showing that his furo is not in a dedicated studio but in a bathroom, housed inside a white IKEA cabinet. He explains that the furo is the enclosed space where freshly lacquered objects are left to cure. The cabinet is partially wood-lined; he acknowledges that a traditional furo is built entirely of mold-resistant wood, but his version is a stopgap built during a period when he could only order from IKEA. The doors have been sealed (adhesive or tape) to prevent moisture escaping.

Understand the curing chemistry

The maker explains that clear urushi does not dry by evaporation. It polymerises using water vapour and oxygen drawn from the surrounding air, catalysed by laccase enzymes present in the sap. This is why a dry environment will not cure the coat and why the furo must maintain high relative humidity. He notes that the process is counter-intuitive to most people's expectation that a liquid 'dries' by losing water.

Inspect the cabinet interior and shelving

The camera shows the open cabinet. Inside, small wooden shelf pieces are fixed to create tiers, keeping objects off the bottom and allowing air circulation. A red cloth and a plastic bin sit on the lowest shelf. Two wooden brush racks hold brushes upright; one rack carries three brushes with blue ferrules and dark handles. The maker points out that the wood inside serves a dual purpose: structural support and a passive moisture reservoir, since wood naturally holds and releases humidity. He cautions that a proper furo should use a wood species resistant to mold.

Retrieve and arrange brushes shown, not narrated

The maker crouches before the open cabinet and reaches into the upper shelf area to access the brush racks. He lifts one rack, displaying three brushes, and compares it with the second rack already inside. The brushes are stored upright in the humid environment, presumably to keep the bristles from drying or deforming. A red cloth is visible on the bottom shelf, and pump bottles and a glass bottle sit on top of the cabinet (likely lacquer or thinner).

Prepare the humidity-regulating gel

The maker holds a dark grey rectangular tray containing a clear, viscous gel and tilts it to pour the contents into a white container. On-screen text identifies it as 'Gel for humidor from cigar shop.' He explains that the product was purchased as a small quantity of dry salt and dust (roughly 5 ml) that, once hydrated, expands into a large volume of gel. The gel is designed to hold a stable relative humidity (approximately 75 %) and is placed inside the furo as a passive humidity buffer. A small red object is visible submerged in the gel within the tray.

When it is rightThe gel should be a clear, thick, non-runny mass that holds its shape in the container without leaking. It should not be watery or crystallised.

When it goes wrongIf the gel has dried out or separated, it will no longer buffer humidity effectively and must be replaced or re-hydrated per the manufacturer's instructions.

Maintain humidity with silver-ion water spray

To raise humidity above the gel's set point (e.g., to 85 % for a few hours), the maker does not use plain tap water. Instead he uses a silver-ion-infused water product also sourced from a cigar shop, chosen because the silver ions inhibit mold, bacteria, and other microbial growth in the enclosed, humid space. He loads a gardening atomizer or simple spray bottle with this solution and mists the interior of the cabinet. This allows him to boost RH temporarily without introducing a biological contamination risk to the curing lacquer or the wood.

When it is rightAfter spraying, the interior surfaces should feel damp to the touch but not dripping. The RH reading (if monitored) should climb toward the target (75–85 %) within a short period.

When it goes wrongOver-spraying can cause condensation to drip onto lacquered surfaces, creating water spots or disturbing a still-tacky coat. If this happens, remove the object, blot gently, and allow the excess moisture to evaporate before re-entering the furo.

Note the target conditions and future plans

The maker states his working parameters: relative humidity between 70 and 90 %, temperature around 23–25 °C. In his bathroom the ambient temperature runs slightly below that range, but he has been able to hold RH near 75 % consistently and can push it to 85 % for several hours when needed. He mentions that a high-quality raw lacquer can fully polymerise in as little as 6 hours under ideal conditions, but he keeps pieces in the furo for a minimum of 12 to 24 hours as a safety margin. He outlines a planned next version: a larger, fully wooden furo with two separate chambers for two different humidity levels, and a future video explaining how humidity affects curing at different stages.