The structural backbone of Persian Ourosi is the *Gereh-Chini* (wood knot weaving) lattice, constructed from slow-grown Oriental plane tree (*Chenar*) and Persian walnut (*Gerdoo*). Thousands of miniature wooden bars are shaped with half-lap halving joints, tenons, and side-routing grooves, interlocking without glue to form self-supporting Islamic geometric star lattices.
At a Glance: Key Takeaways
- Wood Species: Oriental Plane Tree (Platanus orientalis) & Persian Walnut (Juglans regia)
- Bar Dimensions: Typical cross-section: 7–10 mm wide by 12–15 mm deep
- Groove Specification: Central rebate 1.5mm wide x 2.0mm deep on both lateral sides
- Joinery Mechanics: Dry tongue-and-groove, mitred bridle laps, and housed tenons
- Tolerances: Micron-level hand plane tolerances (<0.05mm deviation)
- Surface Finish: Raw burnished timber sealed with boiled walnut oil or clear sandarac
Timber Conversion and the Excellence of Chenar
The choice of wood for Ourosi is governed by strict mechanical criteria. Softwoods like pine or fir are unacceptable because their alternating soft earlywood and hard latewood rings tear when cut with delicate micro-tenons. Persian carpenters rely on Chenar (Oriental Plane Tree) and old-growth Walnut:
- Interlocked Grain Structure: Oriental plane wood features interlocked, diffuse-porous grain that resists splitting when tiny 1.5mm tenons are cut into bar ends.
- Medullary Ray Brilliance: When quarter-sawn, Chenar displays vibrant medullary ray flecks (lacewood figure) that shimmer with golden chatoyancy when finished with natural oils.
- Zero Torsional Twist: Aged walnut possesses legendary dimensional stability, ensuring that lattice bars remain straight and flat across large multi-meter window spans.
Micro-Tooling and the Mathematics of Gereh-Chini Joinery
In a complex 12-point star Gereh lattice, a single window can contain over 8,000 individual wooden elements. Traditional carpenters executed these without modern CNC routers using specialized hand planes:
1. The Scratch Stock Plane (Khat-Kash): A wooden hand plane fitted with a custom ground-steel cutter profiled to scrape the exact 1.5mm wide by 2mm deep glass groove down the center of long timber strips.
2. Angle Mitre Blocks (Zaviyeh-Kash): Wooden miter boxes cut to exact Islamic geometric angles (36°, 72°, 108° for decagrams; 30°, 60°, 120° for dodecagrams). Carpenters sawed bar ends at these precise angles, ensuring that when three or four struts meet at a star node, their shoulders meet with zero light gap.
Plane Tree and Walnut Tongue-and-Groove Lattice Framing in Ourosi Architectural Decision Matrix
Use this reference table to calculate exact physical dimensions, ratios, and specifications before purchasing:
| Joinery Element | Persian Term | Tool Used | Angle / Dimension | Structural Role |
|---|---|---|---|---|
| Lattice Bar Slat | Lochik / Shamseh | Scratch plane & pull-saw | 8 x 12 mm stock | Primary geometric arm |
| Rebate Groove | Kanal-e Shisheh | Custom steel blade scraper | 1.5mm wide x 2.0mm deep | Encapsulates colored glass |
| Star Joint Node | Gereh-gah | Fine Japanese-style pull-saw | 36° / 72° / 108° mitres | Interlocking radial star center |
| Outer Tenon Tongue | Zabaneh | Framing chisel & rasp | 3mm long tongue | Locks into outer sash frame dado |
Practical Constraints
Every successful decoration project must account for physical and environmental constraints:
Extremely High Part Count Labor
Saw Blade Kerf Loss
Milling and Assembling Lattice Bars for a Gereh Medallion
Execute this professional sequence to achieve flawless results without backtracking:
Quarter-Sawing Timber
Rip dry walnut logs into quarter-sawn boards to guarantee radial grain orientation; plane to 8mm thickness.
Batch Grooving
Draw the scratch-stock plane down both sides of each board to plow the 1.5mm glass rebate groove along the entire length.
Slat Ripping
Rip the grooved boards into 12mm-wide individual lattice slats using a fine-kerf table saw or hand frame saw.
Angular Cross-Cutting
Place slats in precision angle mitre blocks; cut segments to length based on the geometric template using a fine-toothed dozuki saw.
Node Notching
Chisel half-lap notches at mid-points where lattice bars intersect, checking that mating pieces slide together with snug hand pressure.
Pre-Assembly Dry Test
Assemble a test star module without glass to verify that angles close into a mathematically perfect 360-degree loop.
Common Mistakes & Countermeasures
Avoid these costly errors that compromise aesthetics, ergonomics, and budget:
Using flat-sawn timber with tangential grain
Applying wood glue into the lattice joints
Divergent groove depths across different slats
Project Execution Checklist
Track your physical progress. Checkboxes persist automatically on this device:
Frequently Asked Questions
Why are there no metal pins or brads in the lattice intersections?
Metal nails corrode, stain the wood, and create rigid localized anchor points that split delicate 8mm wooden struts during thermal expansion. The friction fit of interlocking wood joints combined with outer sash clamping provides superior longevity without metal fasteners.
How are Ourosi windows cleaned without disassembling the intricate wood pieces?
Traditional Persian households clean Ourosi windows using soft dry camel-hair brushes and gentle bellows to blow away desert dust, followed by light rubbing with a cloth dampened in walnut oil to nourish the wood.
