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Introduction to the Imperial “Golden Brick” Manufacturing Process in Ancient China Brictec – Clay Brick Technology Insight Series  I. Overview and Historical BackgroundThe so-called “Golden Brick” (Jinzhuan) was not made of real gold. It was a high-grade square clay brick specially produced during the Ming and Qing Dynasties for imperial palaces such as the Forbidden City’s three main halls. Renowned for its smooth luster, dense texture, and metallic resonance, it was also called Jing Brick or Fine Clay Palace Brick. Historical records indicate several standard sizes (e.g., 1.7 chi or 2.2 chi in length), and it was mainly used for floor paving in imperial halls and other royal venues. The production of Golden Bricks was extremely complex and time-consuming, with a manufacturing cycle exceeding one year. In modern times, this process has been recognized as an Intangible Cultural Heritage of China. II. Raw Material Sources and Selection — Why It Is Unique 1.Origin:Traditionally sourced from Suzhou, Jiangsu Province, especially from areas such as Lumu Imperial Kiln Village and Taihu Lake mud. The fine-grained, iron-rich lakebed clay from the Jiangnan region was known for being “sticky but not loose, powdery but not sandy,” ideal for making dense, glossy brick bodies. Historical kiln records confirm this provenance. 2.Material Requirements:The clay had to be fine-grained and low in impurities, with strict control of iron content, plasticity, cohesion, and organic matter. Since natural deposits varied, multiple clays were often blended to achieve the desired plasticity and firing color. III. Overall Production Cycle and Key Stages 1.Historical and archaeological studies agree that Golden Brick production was a long, multi-stage process that included: Soil selection → Clay refining (settling, filtering, drying, kneading, treading, etc.) → Molding → Natural drying → Kiln firing → Water curing (“Yinshui”) → Polishing and finishing. 2.The entire cycle typically exceeded one year, with some records citing 12–24 months from clay preparation to finished brick. The clay refining process alone often lasted for several months. Some documents describe 29 detailed sub-steps in total. IV. Step-by-Step Technical Process (Grouped by Stage) Note: Details varied by historical period and kiln site. The following represents common, technically refined practices documented by museums and scholarly research. 1. Raw Clay Pre-Treatment (Extraction → Mixing → Settling and Clarification) Clay extraction: Selected from lake mud or designated pits, avoiding sand and organic-rich layers. Coarse screening: Removed stones, roots, and large debris. Soaking and sedimentation (“Cheng”): Clay was soaked for long periods; gravity settling separated fine particles from impurities. Filtering and water replacement (“Lü”): Multiple filtrations and water changes improved particle uniformity and purity. Technical significance: Determines particle grading and purity, fundamental for the brick’s density and surface gloss. 2. Clay Refining (Long-Term Aging and Kneading) Drying and airing (“Xi”): Partially dried to suitable moisture for kneading. Kneading and treading (“Le” & “Ta”): Manual or foot kneading expelled air, improved cohesion, and homogenized texture. Repeated clay refining: Historical records emphasized repetition — months of repeated mixing, filtering, and aging. Technical significance: Long-term aging (analogous to modern “clay maturation”) improves plasticity, reduces internal stress, and ensures uniform shrinkage and dense firing—the key to the Golden Brick’s unique “metallic sound.” 3. Forming and Compaction Molds and pressing: Large square molds were used. Workers manually pressed or stepped on boards to compact clay evenly. Stamping and surface finishing: Some bricks bore imprints or royal stamps. Surfaces were carefully smoothed. Technical significance: Manual compaction and surface polishing created dense, smooth, low-porosity bricks. 4. Natural Drying and Controlled Air-Drying Long-term air-drying: Instead of fast drying, bricks were slowly air-dried for 5–8 months, minimizing cracks. Technical significance: Slow moisture release prevented shrinkage cracks and ensured even internal moisture before firing. 5. Kiln Loading and Long-Term Firing Kiln type and stacking: Imperial kilns like those at Lumu were large and meticulously managed. Stacking patterns optimized heat distribution. Slow temperature rise and long soaking: Firing took weeks or months, avoiding thermal shock and crystal stress. “Yinshui” water curing: Post-firing, bricks were soaked in water basins to stabilize structure and enhance the metallic resonance. Technical significance: Controlled, slow high-temperature firing plus water curing increased strength, density, and acoustic quality. 6. Post-Firing Finishing (Polishing, Sorting, Acceptance) Cooling and inspection: Bricks were cooled and manually inspected. Qualified ones were glossy, crack-free, and resonant when struck. Polishing and trimming: Edges were refined and polished before installation in palace halls. V. Why Were Golden Bricks of Such Exceptional Quality? Extended clay refining and aging: Months of clarification and maturation yielded fine, pure, cohesive clay for high densification. Slow drying and firing: Prevented cracking and ensured homogeneous internal structure. Unique mineral composition: Iron content enhanced surface color and solid-phase reactions, improving hardness and hue. Post-treatment (water curing & polishing): Enhanced surface gloss, density, and acoustic resonance (“metallic sound”). VI. Comparison Between Imperial Golden Bricks and Modern Clay Sintered Bricks Item Ancient Imperial “Golden Brick” Modern Tunnel Kiln Clay Brick Raw Material Processing Special clay from designated sites; months of clarification and kneading Mechanized crushing, blending, and mixing (hours to days) Forming Method Manual molding and board pressing Vacuum extrusion and continuous cutting (automated, high output) Drying Long-term natural drying (months) Mechanical tunnel drying (hours to days) Firing Traditional kilns with slow heating, long soaking, and water curing (weeks–months) Tunnel or roller kiln; continuous and precisely controlled (hours) Productivity & Yield Very low output, low yield but supreme quality High output, standardized, stable yield Quality Features Extremely dense, glossy surface, metallic resonance High strength, consistent dimensions, controllable absorption Labor Intensity Labor-intensive, craft-based, long cycle Mechanized/automated, efficient, short cycle Comment:Ancient Golden Brick production pursued ultimate craftsmanship and imperial aesthetics, trading enormous manual effort and time for rarity and perfection.Modern brickmaking focuses on scalability, uniformity, and cost efficiency, achieved through mechanization, automation, and quality control systems. VII. Material Science and Acoustic Interpretation — Why Does It “Ring Like Metal”? The Golden Brick’s “metallic sound” arises from its high density, low porosity, and high elastic modulus.When internal particles are tightly sintered with minimal pores, impact stress waves propagate with low energy loss, producing a clear, bright tone similar to ceramics or stone.Long-term clay aging, water curing, and surface polishing further enhance this acoustic effect. VIII. Institutional Legacy and Cultural Preservation The Golden Brick technique has been listed as an Intangible Cultural Heritage of China.Today, artisans in Suzhou and Lumu Imperial Kiln Museum continue to preserve and reproduce this craft for heritage restoration and cultural education. IX. Technical Significance The superior performance of imperial Golden Bricks stems from the synergy of four factors: Clay selection; Extended refining and maturation; Controlled slow drying and firing; Post-firing water curing and polishing.Together, they yield extremely low porosity and exceptional density. Compared with modern industrial brickmaking, Golden Brick production sacrifices productivity and cost for ultimate quality, representing the pinnacle of manual craftsmanship and experiential control.Modern production prioritizes efficiency, consistency, and standardization — two technological paths reflecting different eras. In preservation and restoration, understanding and retaining key traditional steps — especially clay aging, slow drying, and water curing — is vital for replicating the authentic quality of historical palace bricks. Brictec – Clay Brick Technology Insight SeriesWritten by: JF & Lou

Refractory Bricks for Tunnel Kilns in Clay Sintered Brick Plants Tunnel kilns are continuous high-temperature firing systems characterized by long structures and multiple thermal zones. Each section operates under different temperature, atmosphere, and mechanical stress conditions. Therefore, the proper selection and configuration of refractory bricks are critical for kiln performance, energy efficiency, and service life. I. Types and Properties of Refractory Bricks Used in Tunnel Kilns 1. Main Types by Material No. Refractory Type Major Composition Service Temperature (°C) Main Features Typical Applications 1 High Alumina Brick Al₂O₃ ≥ 55% 1300–1600 High compressive strength, good slag resistance, poor thermal shock resistance Firing zone roof, kiln door, flame-contact areas 2 Mullite Brick 3Al₂O₃·2SiO₂ 1350–1700 Low thermal expansion, excellent thermal shock resistance, no deformation Firing zone roof and wall, insulation zone 3 Cordierite Brick 2MgO·2Al₂O₃·5SiO₂ 1250–1400 Very low thermal expansion, excellent thermal shock resistance Lower firing zone, transition area 4 Lightweight High Alumina Brick Porous Al₂O₃ ≥ 50% ≤1350 Lightweight, excellent insulation Insulation layer, secondary wall, roof upper layer 5 Fire Clay Brick Al₂O₃ 30–45% 1200–1350 Economical, easy to construct, moderate thermal shock resistance Preheating zone, outer wall, flue lining 6 Insulating Brick SiO₂–Al₂O₃ ≤1100 Low thermal conductivity, lightweight Outer wall insulation layer 7 Silica Brick SiO₂ ≥ 95% 1650–1700 Excellent creep resistance at high temperature, acid-resistant Upper roof of firing zone, kiln head 8 Wear-Resistant Brick High-alumina or mullite-based composite ≤1400 Excellent abrasion and impact resistance Car wheel zone, track edge, kiln car top 9 Silicon Carbide Brick (SiC) SiC ≥ 70% 1500–1650 High thermal conductivity, oxidation and erosion resistance Burner zone, flame impact area, car base 10 Castable / Precast Block High alumina, mullite, or SiC-based 1300–1600 Good integrity and air-tightness Burner ports, arches, sealing joints 11 Ceramic Fiber Board / Blanket Al₂O₃ + SiO₂ ≤1400 Lightweight, excellent insulation, easy installation External insulation, kiln doors, wall lining 12 Shaped / Custom Brick Custom composition Varies Precision fit, customized geometry Burner brick, arch foot, transition pieces   II. Refractory Configuration and Construction Standards in Tunnel Kiln Design 1. Recommended Material Configuration by Kiln Section Kiln Section Recommended Brick Types Thickness (mm) Temperature (°C) Description Roof (Firing Zone) Mullite / Cordierite + Lightweight High Alumina + Ceramic Fiber 500–550 1250–1300 Combines high strength and insulation Wall (Firing Zone) High Alumina / Mullite + Lightweight Alumina + Fiber Board 500 1200–1300 Inner heat-resistant, outer insulating Wall (Preheating Zone) Fire Clay + Lightweight Alumina 400–500 900–1100 Emphasizes thermal shock resistance Insulation Zone Cordierite + Insulating Brick 400 900–1000 Reduces heat loss Flue Lining Fire Clay / SiC Brick 250–350 800–1000 High erosion resistance Kiln Door / Sealing Panels Mullite + Fiber Board + Steel Plate 450–500 1100–1200 Combines insulation and mechanical strength Kiln Car Surface Cordierite / SiC / High Alumina Brick 230 1000–1250 Load-bearing and wear-resistant Kiln Car Insulation Layer Insulating Brick + Ceramic Fiber 200–250 ≤900 Reduces heat conduction Burner Port / Arch Foot SiC / Castable Blocks Custom 1300–1500 High thermal shock and erosion resistance   2. Construction and Masonry Standards Item Technical Requirements Brick Joints ≤ 2 mm; staggered joints ≥ 1/4 brick length Anchoring Stainless steel anchors every 5 brick layers Mortar Use matching refractory mortar (same base material) Construction Sequence Build walls first, then arches; inner lining before outer layer Drying & Heating-Up Initial heating rate ≤ 30°C/hour to prevent cracks Arch Control Accurate curvature control to avoid stress concentration Joints Sealing High-temp sealing compound or ceramic fiber filling   III. Standards for Qualified Refractory Materials 1. Appearance and Dimensional Tolerance (per GB/T 2992.1, GB/T 16544) Item Requirement Surface Smooth, no cracks, chips, or dense pores Dimensional Tolerance ±2 mm in length, width, and height Density Uniformity ≤ ±0.05 g/cm³ variation within the same batch   2. Physical and Chemical Properties (Ref. GB/T 3995, GB/T 10325) Property High Alumina Mullite Cordierite Fire Clay Bulk Density (g/cm³) 2.3–2.6 2.4–2.7 1.9–2.2 2.0–2.2 Apparent Porosity (%) 18–22 15–20 25–30 22–26 Cold Crushing Strength (MPa) ≥60 ≥70 ≥45 ≥35 Permanent Linear Change (%) ±0.2 ±0.3 ±0.3 ±0.4 Refractoriness Under Load (°C) ≥1450 ≥1600 ≥1400 ≥1350 Thermal Shock Resistance (cycles 900°C–water) ≥20 ≥25 ≥30 ≥15   3. Inspection and Acceptance Procedure Raw Material Inspection Chemical composition (Al₂O₃, SiO₂, Fe₂O₃ content) Phase analysis (XRD test) Finished Product Testing Dimensional and visual inspection Fired bulk density and compressive strength test Thermal shock resistance test Documentation Factory test report with chemical and physical data Quality certificate compliant with GB/T, ISO, or ASTM standards On-site Verification Random sampling of ≥10% for re-test before use Only approved materials may be used in kiln construction   IV. Selection Principles for Refractory Materials Principle Description Temperature Matching Select materials according to thermal zones and service temperature Thermal Shock Resistance Priority Roofs and burner zones require mullite or cordierite bricks Mechanical Strength Coordination Use high alumina or SiC bricks for load-bearing areas Insulation Coordination Combine dense inner bricks with lightweight outer layers Supplier Qualification Must hold ISO/GB certification and third-party test reports Sample Verification New suppliers must pass firing performance tests before approval   Conclusion A well-designed refractory system ensures: Stable tunnel kiln operation Low energy consumption Extended kiln service life Consistent product quality Proper selection and configuration of refractory bricks are fundamental to the success of modern clay sintered brick plants and to the overall efficiency of tunnel kiln construction projects.

Xi’an Brictec Iraq KTB Project Enters Accelerated Construction Phase October 2025 Construction Progress Report Project Overview: The project is planned to build three modern tunnel kiln-fired brick production lines, implemented in three phases. After the commissioning of Phase I and Phase II, Xi’an Brictec, following its participation in the Sulaymaniyah Najimadin project, has launched its second turnkey clay brick project in Iraq. The designed production capacity is 1,200 tons/day, covering Iraq’s mainstream brick types — mainly 240×115×75mm, 400×200×200mm, and 200×200×400mm clay fired bricks. At the end of September 2025, the General Manager of Xi’an Brictec personally visited the project site to inspect the construction progress, communicate with the client, and review project updates to ensure the project is completed on time, with guaranteed quality and quantity. KTB Project October 2025 Construction Progress Report In October 2025, the construction of the KTB project has been progressing steadily. The current status is as follows: 1. Construction Team A total of nine professional construction workers from Brictec were dispatched to the project. All of them have many years of experience in brick plant construction and kiln installation, providing solid manpower and technical support for on-site operations. 2. Tunnel Kiln Construction Progress As the core facility of the brick plant, the tunnel kiln’s progress is of utmost importance. Since early September, Xi’an Brictec has assigned skilled masons to accelerate the kiln wall construction. Currently, the kiln wall masonry is well underway, and construction quality strictly follows brick plant standards, ensuring the kiln’s stability, durability, and insulation performance, laying a solid foundation for subsequent installation and operation. 3. Return Line Construction Progress The foundation work of the return line is being carried out as planned according to the process design drawings. The progress is on schedule, and the bearing capacity and stability of the foundation fully meet the design requirements, providing reliable support for future rail installation and kiln car operation. 4. Clay Aging Storage Construction Progress The foundation treatment for the clay aging storage area is also being accelerated. It ensures sufficient load-bearing capacity and strict quality control, laying a firm foundation for the later construction and clay aging storage operations. 5. Next Work Plan The project team will maintain efficient construction, strengthen on-site management, and ensure both quality and safety. Meanwhile, the team will closely monitor weather and other external factors, arrange schedules reasonably, and ensure that the project is completed on time and to high standards. The KTB project team will continue to uphold a professional, efficient, and responsible attitude, fully dedicated to building a high-quality brick plant project. Keywords: Mullite refractory materials, lightweight mullite bricks, tunnel kiln insulation cotton, kiln car bricks, tunnel kiln, dryer.