Metallic luster crystalline glaze with rusted edge effect, ceramic tile and preparation method thereof

Abstract

The present application relates to the technical field of ceramic tiles, and particularly relates to a metal luster crystalline glaze with rusted edge effect, a ceramic tile and a preparation method thereof. The preparation raw materials of the metal luster crystalline glaze include, by mass percentage, 35-45% of potassium feldspar, 5-12% of calcite, 5-12% of calcined talc, 8-18% of calcined zinc oxide, 10-20% of titanium white, 6-16% of black clay powder, 2-8% of frit, and 8-17% of iron oxide. The metal luster crystalline glaze takes titanium white and iron oxide as the core, forms a glaze layer with the metal luster of golden sand after firing, and realizes the metal effect by using non-noble metal.

Description

Technical Field

[0001] This invention relates to the field of ceramic tile technology, and in particular to a metallic luster crystalline glaze with a rust edge effect, a ceramic tile, and a method for preparing the same. Background Technology

[0002] Traditional metallic glaze ceramic tiles have the following drawbacks: First, the metallic effect relies on expensive metal oxides as colorants, resulting in high overall production costs and making large-scale promotion difficult. Second, they have poor chemical stability; the metallic crystal phase is prone to oxidation and fading, and their resistance to ultraviolet aging is weak, leading to glaze loss and rust effect peeling after long-term use. Third, the decorative effect is limited; imitation rust textures often rely on secondary printing, sandblasting, or manual processing, which are cumbersome and inconsistent. Fourth, the glaze layer and the body have insufficient bonding strength, making them prone to defects such as delamination, peeling, and cracking, resulting in a low product qualification rate.

[0003] It is evident that existing technologies still need improvement and enhancement. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a metallic luster crystalline glaze with rust edge effect, ceramic tile and its preparation method, aiming to solve the technical problems in the prior art such as the reliance on high-valence metal oxides as colorants to present the metallic effect of metallic glaze ceramic tiles.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of the present invention provides a metallic luster crystalline glaze with a rust edge effect. The raw materials for preparing the metallic luster crystalline glaze, by mass percentage, include: 35-45% potassium feldspar, 5-12% calcite, 5-12% calcined talc, 8-18% calcined zinc oxide, 10-20% titanium dioxide, 6-16% black mud powder, 2-8% frit, and 8-17% iron oxide.

[0006] The metallic luster crystalline glaze with rust edge effect, wherein, by mass percentage, the chemical composition of the frit includes: 61-63% SiO2, 7-8% Al2O3, 15-17% CaO, 5-7% B2O3, 4-5% MgO, 1.8-2.0% K2O, and 1.1-1.4% Na2O.

[0007] The aforementioned metallic luster crystalline glaze with a rust-edge effect, wherein the melting temperature of the frit is 1170–1190°C, and its high-temperature viscosity at 1230°C is 110–130 Pa. s.

[0008] A second aspect of the present invention provides a ceramic tile comprising a tile body layer, a base glaze layer, and a top glaze layer arranged sequentially; the top glaze layer is obtained by firing the metallic luster crystalline glaze described above.

[0009] The ceramic tile, wherein the base glaze layer is obtained by firing a base glaze, and the raw materials for preparing the base glaze, by mass percentage, include: 25-35% potassium feldspar, 35-45% sodium feldspar, 5-15% calcined talc, 5-15% calcined kaolin, and 5-15% black mud powder.

[0010] The third aspect of this invention discloses a method for preparing ceramic bricks, comprising the following steps: S1. Apply a base glaze to the brick blank to form a base glaze layer after firing. The raw materials for preparing the base glaze, by mass percentage, include: 25-35% potassium feldspar, 35-45% sodium feldspar, 5-15% calcined talc, 5-15% calcined kaolin, and 5-15% black mud powder. S2. Apply the metallic crystalline glaze as described above to form a surface glaze layer after firing; S3. Dry and fire to obtain ceramic bricks as described above.

[0011] In the method for preparing ceramic tiles, the specific gravity of the base glaze slurry is 1.35–1.45 g / cm³. 3 The glaze application amount is 1.0–1.6 g / 2300 mm. 2 .

[0012] In the method for preparing the ceramic tile, the specific gravity of the glaze slurry in the base glaze is 1.62–1.72 g / cm³. 3 The glaze application amount is 2.3–3.3 g / 2300 mm. 2 .

[0013] The method for preparing ceramic bricks, wherein the firing temperature is 1180–1230℃ and the firing cycle is 38–42 min.

[0014] In the method for preparing ceramic tiles, the fineness of the glaze slurry of the base glaze and the metallic luster crystalline glaze is 0.2-0.5% residue on a 325-mesh sieve.

[0015] Beneficial Effects: This invention provides a metallic crystalline glaze with a rust-edge effect. The glaze uses iron oxide and titanium dioxide as the core coloring and nucleating agents, combined with the fluxing and phase-regulating effects of calcined zinc oxide. During high-temperature firing, a composite metallic crystal phase of ilmenite (FeTiO3) and zinc-iron spinel (ZnFe2O4) is generated in situ, exhibiting a sand-gold-like metallic luster. This metallic effect is achieved using non-precious metals. Furthermore, the metallic crystalline glaze of this invention also achieves an edge-like rust texture without the need for additional printing or other processes, achieving multiple effects with a single glaze. Attached Figure Description

[0016] Figure 1 This is a physical image of Example 1.

[0017] Figure 2 This is a physical image of Example 2.

[0018] Figure 3 This is a physical image of Example 3.

[0019] Figure 4 This is a physical image of Comparative Example 1.

[0020] Figure 5 This is a physical image of Comparative Example 2.

[0021] Figure 6 This is a physical image of Comparative Example 3.

[0022] Figure 7 This is a physical image of Comparative Example 4.

[0023] Figure 8 This is a photograph of the actual object in Comparative Example 5.

[0024] Figure 9 This is a physical image of Comparative Example 6. Detailed Implementation

[0025] This invention provides a metallic luster crystalline glaze with a rust-edge effect, a ceramic tile, and a method for preparing the same. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0026] The first aspect of the present invention provides a metallic luster crystalline glaze with a rust edge effect. The raw materials for preparing the metallic luster crystalline glaze, by mass percentage, include: 35-45% potassium feldspar, 5-12% calcite, 5-12% calcined talc, 8-18% calcined zinc oxide, 10-20% titanium dioxide, 6-16% black mud powder, 2-8% frit, and 8-17% iron oxide.

[0027] In this metallic crystalline glaze, iron oxide and titanium dioxide serve as the core coloring and nucleating agents. Combined with the fluxing and phase-regulating effects of calcined zinc oxide, a composite metallic crystalline phase of ilmenite (FeTiO3) and zinc-iron spinel (ZnFe2O4) is generated in situ during high-temperature firing, resulting in a sandy gold metallic luster. This eliminates the need for high-valence metal oxides as colorants, effectively reducing production costs. Furthermore, this invention utilizes the difference between the glaze edge and interior to induce a gradient oxidation-reduction reaction in iron oxide. The interior of the glaze generates a composite crystalline phase of ilmenite and zinc-iron spinel, presenting a uniformly dispersed, micron-sized, golden-red sandy gold shimmering texture. At the glaze edge, a mixed crystalline phase of Fe2O3 (reddish-brown) and Fe3O4 (black) forms a brownish-red rust texture with alternating light and dark shades and a natural transition. Simultaneously, the surface tension of the glaze creates a slightly uneven texture at the edges, simulating the visual and tactile effects of natural metal corrosion. The surface tension of the glaze layer creates a slightly textured edge, eliminating the need for secondary printing, sandblasting, or manual processing. A single glaze achieves multiple effects, effectively reducing costs and solving the problem of separation and detachment of different effect layers in traditional composite decorative processes. However, when the iron oxide content is too low, the metallic texture and border effect are substandard; when the iron oxide content is too high, it leads to increased surface pinhole defects and a lower yield. Furthermore, too low a titanium dioxide content can cause glaze runs and poor border effects; too high a content can lead to glaze shrinkage and insufficient metallic texture. The content of calcined zinc oxide also significantly affects the glaze layer. When the calcined zinc oxide content is too low, the glaze layer is not fully sintered and prone to cracking; if the content is too high, it can lead to excessive melting of the glaze layer and numerous pinholes.

[0028] Among the other components mentioned above, the frit and potassium feldspar form a low-temperature eutectic system, resulting in a firing temperature of 1180–1220℃, which is 20–30℃ lower than that of traditional metallic glazes, thus reducing production costs. Furthermore, potassium feldspar and frit can form a continuous and uniform glassy phase matrix. Ilmenite-type and zinc-iron spinel-type composite crystalline phases are uniformly dispersed in the glassy phase as micron-sized particles, forming a dense structure of "glassy phase encapsulating crystalline phase," effectively blocking the penetration of external corrosive media and improving the glaze's resistance to acid and alkali corrosion. Due to the stable chemical properties of the composite crystalline phase, its resistance to ultraviolet aging is also higher than that of traditional metallic glazes, and the rust border is composed of a stable iron oxide crystalline phase, showing no fading or peeling even after long-term use. Black mud powder has a plasticity-improving effect, used to improve the suspension and application performance of the glaze slurry.

[0029] Preferably, the chemical composition of the fused block, by mass percentage, includes: 61-63% SiO2, 7-8% Al2O3, 15-17% CaO, 5-7% B2O3, 4-5% MgO, 1.8-2.0% K2O, and 1.1-1.4% Na2O.

[0030] Preferably, the melting temperature of the frit is 1170–1190°C, and its high-temperature viscosity at 1230°C is 110–130 Pa. s.

[0031] A second aspect of the present invention provides a ceramic tile comprising a tile body layer, a base glaze layer, and a top glaze layer arranged sequentially; the top glaze layer is obtained by firing the metallic luster crystalline glaze described above.

[0032] Preferably, the base glaze layer is obtained by firing a base glaze, and the raw materials for preparing the base glaze, by mass percentage, include: 25-35% potassium feldspar, 35-45% sodium feldspar, 5-15% calcined talc, 5-15% calcined kaolin, and 5-15% black mud powder. The base glaze with the above formula has a coefficient of thermal expansion between that of the brick body and the metallic crystalline glaze, forming a continuous gradient distribution of the coefficient of thermal expansion, eliminating interfacial stress concentration; at the same time, the base glaze forms a dense intermediate barrier layer, preventing impurities in the brick body from migrating to the metallic crystalline glaze.

[0033] The third aspect of this invention discloses a method for preparing ceramic bricks, comprising the following steps: S1. Apply a base glaze to the brick blank to form a base glaze layer after firing. The raw materials for preparing the base glaze, by mass percentage, include: 25-35% potassium feldspar, 35-45% sodium feldspar, 5-15% calcined talc, 5-15% calcined kaolin, and 5-15% black mud powder. S2. Apply the metallic crystalline glaze as described above to form a surface glaze layer after firing; S3. Dry and fire to obtain ceramic bricks as described above.

[0034] Preferably, the specific gravity of the base glaze slurry is 1.35–1.45 g / cm³. 3 The glaze application amount is 1.0–1.6 g / 2300 mm. 2 The specific gravity of the base glaze slurry is 1.62–1.72 g / cm³. 3 The glaze application amount is 2.3–3.3 g / 2300 mm. 2 When glazing, applying too little glaze will result in a thin glaze layer, easily leading to exposed clay and insufficient adhesion; applying too much glaze will easily cause glaze runs and cracking. The specific gravity of the glaze slurry must also be appropriate to ensure good glazing uniformity and a high yield; when the specific gravity is too low, the glaze slurry is prone to sedimentation, resulting in uneven glazing; when the specific gravity is too high, the glaze slurry has poor fluidity, easily leading to an uneven glaze surface.

[0035] Preferably, the firing temperature is 1180–1230℃, and the firing cycle is 38–42 minutes. When the firing temperature is within the range of 1180–1220℃, the product yield is at a relatively high level; when the temperature is below 1180℃, the glaze layer is not fully sintered, the crystal phase is underdeveloped, and problems such as glaze cracking and poor texture are prone to occur; when the temperature is above 1220℃, the glaze layer melts excessively, and defects such as glaze flow and pinholes are prone to occur, resulting in a decrease in the yield.

[0036] Preferably, the fineness of the glaze slurry of the base glaze and the metallic luster crystalline glaze is 0.2-0.5% residue on a 325-mesh sieve.

[0037] The present invention will be further illustrated by the following examples and comparative examples.

[0038] Example 1 A ceramic brick, the preparation method of which includes the following steps: S1. Apply a base glaze to the brick blank to form a base glaze layer after firing. The raw materials for preparing the base glaze, by mass percentage, include: 30% potassium feldspar, 40% sodium feldspar, 10% calcined talc, 10% calcined kaolin, and 10% black clay powder; the specific gravity of the base glaze slurry is 1.35 g / cm³. 3 Glazing amount is 1.0g / 2300mm 2 ; S2. Apply a metallic crystalline glaze to form a surface glaze layer after firing; the raw materials for preparing the metallic crystalline glaze, by mass percentage, include: 40% potassium feldspar, 6% calcite, 6% calcined talc, 12% calcined zinc oxide, 13% titanium dioxide, 7% black clay powder, 4% frit, and 12% iron oxide; the specific gravity of the metallic crystalline glaze slurry is 1.67 g / cm³. 3 Glazing amount: 2.8g / 2300mm 2 ; The chemical composition of the fused block, by mass percentage, includes: 62.3% SiO2, 7.6% Al2O3, 16.2% CaO, 5.9% B2O3, 4.8% MgO, 1.9% K2O, and 1.3% Na2O. S3. Drying and firing at 1200℃ for 40 minutes to obtain the ceramic brick.

[0039] Example 2 A ceramic brick, the preparation method of which includes the following steps: S1. Apply a base glaze to the brick blank to form a base glaze layer after firing. The raw materials for preparing the base glaze, by mass percentage, include: 25% potassium feldspar, 35% sodium feldspar, 15% calcined talc, 15% calcined kaolin, and 10% black clay powder; the specific gravity of the base glaze slurry is 1.35 g / cm³. 3Glazing amount is 1.0g / 2300mm 2 ; S2. Apply a metallic crystalline glaze to form a surface glaze layer after firing; the raw materials for preparing the metallic crystalline glaze, by mass percentage, include: 35% potassium feldspar, 5% calcite, 5% calcined talc, 8% calcined zinc oxide, 17% titanium dioxide, 8% black clay powder, 5% frit, and 17% iron oxide; the specific gravity of the metallic crystalline glaze slurry is 1.72 g / cm³. 3 The glaze application amount is 3.3g / 2300mm. 2 ; The fused block is the same as in Example 1; S3. Drying and firing at 1220℃ for 42 minutes to obtain the ceramic brick.

[0040] Example 3 A ceramic brick, the preparation method of which includes the following steps: S1. Apply a base glaze to the brick blank to form a base glaze layer after firing. The raw materials for preparing the base glaze, by mass percentage, include: 35% potassium feldspar, 45% sodium feldspar, 5% calcined talc, 5% calcined kaolin, and 10% black mud powder; the specific gravity of the base glaze slurry is 1.35 g / cm³. 3 Glazing amount is 1.0g / 2300mm 2 ; S2. Apply a metallic crystalline glaze to form a surface glaze layer after firing; the raw materials for preparing the metallic crystalline glaze, by mass percentage, include: 44% potassium feldspar, 8% calcite, 8% calcined talc, 8% calcined zinc oxide, 10% titanium dioxide, 10% black clay powder, 4% frit, and 8% iron oxide; the specific gravity of the metallic crystalline glaze slurry is 1.62 g / cm³. 3 Glazing amount: 2.3g / 2300mm 2 ; The fused block is the same as in Example 1; S3. Drying and firing at 1200℃ for 40 minutes to obtain the ceramic brick.

[0041] Comparative Example 1 A ceramic tile whose preparation method differs from that of Example 1 is that the formulation of the metallic luster crystalline glaze is different; In this comparative example, the raw materials for preparing the metallic crystalline glaze, by mass percentage, include: 38% potassium feldspar, 5% calcite, 5% calcined talc, 11% calcined zinc oxide, 10% titanium dioxide, 8% black mud powder, 3% frit, and 20% iron oxide.

[0042] Comparative Example 2 A ceramic tile whose preparation method differs from that of Example 1 is that the formulation of the metallic luster crystalline glaze is different; In this comparative example, the raw materials for preparing the metallic crystalline glaze, by mass percentage, include: 43% potassium feldspar, 7% calcite, 7% calcined talc, 14% calcined zinc oxide, 12% titanium dioxide, 8% black mud powder, 4% frit, and 5% iron oxide.

[0043] Comparative Example 3 A ceramic tile whose preparation method differs from that of Example 1 is that the formulation of the metallic luster crystalline glaze is different; In this comparative example, the raw materials for preparing the metallic crystalline glaze, by mass percentage, include: 38% potassium feldspar, 5% calcite, 5% calcined talc, 8% calcined zinc oxide, 22% titanium dioxide, 7% black mud powder, 4% frit, and 11% iron oxide.

[0044] Comparative Example 4 A ceramic tile whose preparation method differs from that of Example 1 is that the formulation of the metallic luster crystalline glaze is different; In this comparative example, the raw materials for preparing the metallic crystalline glaze, by mass percentage, include: 42% potassium feldspar, 7% calcite, 7% calcined talc, 13% calcined zinc oxide, 7% titanium dioxide, 8% black mud powder, 4% frit, and 12% iron oxide.

[0045] Comparative Example 5 A ceramic tile whose preparation method differs from that of Example 1 is that the formulation of the metallic luster crystalline glaze is different; In this comparative example, the raw materials for preparing the metallic crystalline glaze, by mass percentage, include: 38% potassium feldspar, 5% calcite, 5% calcined talc, 20% calcined zinc oxide, 10% titanium dioxide, 7% black mud powder, 4% frit, and 11% iron oxide.

[0046] Comparative Example 6 A ceramic tile whose preparation method differs from that of Example 1 is that the formulation of the metallic luster crystalline glaze is different; In this comparative example, the raw materials for preparing the metallic crystalline glaze, by mass percentage, include: 42% potassium feldspar, 8% calcite, 7% calcined talc, 5% calcined zinc oxide, 12% titanium dioxide, 9% black mud powder, 4% frit, and 13% iron oxide.

[0047] The surface effects of the ceramic tiles in the above embodiments and comparative examples are summarized in Table 1: Table 1

[0048] Table 2 shows the product performance results of the ceramic tiles in the examples and comparative examples.

[0049] Table 2

[0050] The results above show that the metallic crystalline glazes of Examples 1-3 exhibit a distinct metallic texture, clear graininess, and strong shimmering effect after firing. Furthermore, the edges of the glazes form a unique border effect, and the surface is free of defects such as pinholes. In terms of performance, their resistance to acid and alkali corrosion, thermal stability, and Mohs hardness are higher than the comparative examples, while still meeting product requirements, demonstrating good overall performance.

[0051] In the metallic crystalline glaze of Example 2, the content of iron oxide and titanium dioxide is higher, the amount of composite metal crystal phase generated is increased, and the metallic luster is stronger; in addition, the increased glaze application amount expands the edge reaction area and increases the width of the border; the slightly higher firing temperature promotes crystal phase development and the glaze layer is fully sintered.

[0052] In the metallic crystalline glaze of Example 3, the content of iron oxide and titanium dioxide is low, and the amount of composite metal crystal phase generated is moderate; the reduction of glaze application reduces the edge reaction area and narrows the border width; moreover, the slightly lower firing temperature can still meet the requirements for crystal phase formation and glaze sintering.

[0053] Compared with Example 1, the main difference in Comparative Example 1 is that the iron oxide content exceeds the protection scope of the present invention. When the iron oxide content is too high, the reduced crystalline phase inside the glaze layer is excessive, and the edge oxidation reaction is excessive; the high temperature viscosity of the glaze slurry decreases, and the gas does not escape completely during the firing process, forming pinholes.

[0054] Compared with Example 1, the main difference in Comparative Example 2 is that the iron oxide content exceeds the protection scope of the present invention. When the iron oxide content is too low, it is impossible to form a sufficient composite metal crystal phase; the edge oxidation reaction is insufficient, and it is impossible to form obvious rust texture.

[0055] Compared with Example 1, the main difference in Comparative Example 3 is that the titanium dioxide content exceeds the protection scope of the present invention. When the titanium dioxide content is too high, the whiteness of the glass phase increases, which covers the luster of the metallic crystal phase; the surface tension of the glaze slurry is abnormal, which leads to glaze shrinkage during the firing process.

[0056] Compared with Example 1, the main difference of Comparative Example 4 is that the titanium dioxide content exceeds the protection scope of the present invention. When the titanium dioxide content is too low, it is impossible to form a sufficient ilmenite-type crystal phase; the high temperature viscosity of the glaze slurry is too low, and glaze flow occurs during the firing process; the edge crystal phase composition is simple, and the texture effect is poor.

[0057] Compared with Example 1, the main difference in Comparative Example 5 is that the content of calcined zinc oxide exceeds the protection scope of the present invention. When the content of calcined zinc oxide is too high, the fluxing effect is too strong, and the glaze layer melts excessively; a large amount of gas cannot escape in time during the firing process, forming dense pinholes; the crystal phase development is abnormal, and the metallic texture and the edge effect are both affected.

[0058] Compared with Example 1, the main difference in Comparative Example 6 is that the content of calcined zinc oxide exceeds the protection scope of the present invention. When the content of calcined zinc oxide is too low, the glaze layer is not completely sintered; the composite metal crystal phase cannot be formed normally; the thermal expansion coefficient of the glaze layer and the body are poorly matched, resulting in cracking of the glaze surface.

[0059] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. A metallic luster crystalline glaze with a rust-edge effect, characterized in that, The raw materials for preparing the metallic crystalline glaze, by mass percentage, include: 35-45% potassium feldspar, 5-12% calcite, 5-12% calcined talc, 8-18% calcined zinc oxide, 10-20% titanium dioxide, 6-16% black mud powder, 2-8% frit, and 8-17% iron oxide.

2. The metallic luster crystalline glaze with rust edge effect according to claim 1, characterized in that, The chemical composition of the fused block, by mass percentage, includes: 61-63% SiO2, 7-8% Al2O3, 15-17% CaO, 5-7% B2O3, 4-5% MgO, 1.8-2.0% K2O, and 1.1-1.4% Na2O.

3. The metallic luster crystalline glaze with rust edge effect according to claim 2, characterized in that, The melting temperature of the frit is 1170–1190°C, and its high-temperature viscosity at 1230°C is 110–130 Pa. s.

4. A ceramic tile, characterized in that, It includes a brick blank layer, a base glaze layer, and a top glaze layer arranged sequentially; the top glaze layer is obtained by firing the metallic luster crystalline glaze as described in any one of claims 1-3.

5. The ceramic tile according to claim 4, characterized in that, The base glaze layer is obtained by firing a base glaze. By mass percentage, the raw materials for preparing the base glaze include: 25-35% potassium feldspar, 35-45% sodium feldspar, 5-15% calcined talc, 5-15% calcined kaolin, and 5-15% black mud powder.

6. A method for preparing ceramic bricks, characterized in that, Includes the following steps: S1. Apply a base glaze to the brick blank to form a base glaze layer after firing. The raw materials for preparing the base glaze, by mass percentage, include: 25-35% potassium feldspar, 35-45% sodium feldspar, 5-15% calcined talc, 5-15% calcined kaolin, and 5-15% black mud powder. S2. Apply the metallic crystalline glaze according to any one of claims 1-3 to form a surface glaze layer after firing; S3. Dry and fire to obtain the ceramic brick as described in claim 4 or 5.

7. The method for preparing ceramic bricks according to claim 6, characterized in that, The specific gravity of the base glaze slurry is 1.35–1.45 g / cm³. 3 The glaze application amount is 1.0–1.6 g / 2300 mm. 2 .

8. The method for preparing ceramic bricks according to claim 6, characterized in that, The specific gravity of the base glaze slurry is 1.62–1.72 g / cm³. 3 The glaze application amount is 2.3–3.3 g / 2300 mm. 2 .

9. The method for preparing ceramic bricks according to claim 6, characterized in that, The firing temperature is 1180–1230℃, and the firing cycle is 38–42 minutes.

10. The method for preparing ceramic bricks according to claim 6, characterized in that, The fineness of the glaze slurry of the base glaze and the metallic luster crystalline glaze is 0.2-0.5% residue on a 325-mesh sieve.

Images