JP4902896B1 - Silver glaze for lead-free and boron-free roof tiles - Google Patents

Abstract

Provided is a silver lead-free glaze from which components other than lead are removed.
R ¹ ₂ O (R ¹ ₂ O represents one or more of Li ₂ O, Na ₂ O and K ₂ O) is 0.06 mol ≧ R ¹ ₂ O;
0.05 mol ≦ CaO ≦ 0.34 mol of CaO;
Al ₂ O ₃ 0.02 mole ≦ _Al 2 _{O 3} ≦ 0.27 moles;
A silver-free lead-free glaze containing MnO in an amount of 0.65 mol ≦ MnO ≦ 0.95 mol; and TiO ₂ in an amount of 0.11 mol ≦ TiO ₂ and no boron.
[Selection figure] None

Description

  The present invention relates to a silver glaze for lead-free and boron-free roof tiles, that is, a lead-free silver glaze containing no boron.

  Silver tile is a traditional tile, and its color has been widely used since ancient times as a representative color suitable for the Japanese climate, and various glazes (silver glaze) for its production. Things have been developed (Patent Documents 1 to 3). In addition, Patent Document 4 also refers to silver glaze, but the glaze described in that document has a low content (0.38 mol to 0.59 mol) of MnO, which is a main crystal component for silver color development, and silver color. The coloration of is only inadequate.

  In the glaze described in Patent Document 1, lead oxide is used as an indispensable component for silver color development. On the other hand, Patent Literature 2 describes a silver glaze that does not contain lead (silver-colored lead-free glaze), and Patent Literature 3 uses a lead-free technology aimed at improving pollution and the working environment, thereby producing a stable silver color. The lead-free glaze for silver tiles (hereinafter sometimes abbreviated as “silver-colored lead-free glaze”) is described.

To further describe Patent Document 2, in the lead-free silver glaze described in the same document, the total number of moles of alkali metal compounds such as Na ₂ O, Li ₂ O, K ₂ O is reduced to 0.025 mol or less, Penetration is more effectively prevented. In addition, it is described in the same literature that these alkali metal compounds are generally necessary as components of low-temperature soot and become a powerful flux.

Moreover, the lead-free glaze for silver tiles described in Patent Document 3 has the following composition:
R ₂ O total amount ≦ 0.01 mol (where R ₂ O is Li ₂ O, K ₂ O and / or Na ₂ O)
0.1 mol ≦ RO total amount ≦ 0.3 mol (RO is MgO, CaO, SrO and / or BaO)
0.7 mol ≦ MnO ≦ 0.9 mol,
0.1 mol ≦ ZrO ₂ , 0.1 mol ≦ TiO ₂ , ZrO ₂ + TiO ₂ ≦ 1.0,
0.05 mol ≦ Al ₂ O ₃ ≦ 0.3 mol, 0.5 mol ≦ SiO ₂ ≦ 2.5 mol, 4 ≦ SiO ₂ / Al ₂ O ₃ ≦ 25
0.05 mol ≦ B ₂ O ₃ ≦ 0.18 mol

These components are described in Patent Document 3 as follows:
MnO is the main component of the crystal for obtaining a silver color, and when it is less than 0.7 mol, it does not exhibit a good silver color and becomes black. ZrO ₂ and TiO ₂ are essential components that promote crystal formation, ZrO ₂ , Only when TiO ₂ is present at the same time as MnO, the soot exhibits a silver color. Since it has been found that glaze containing ZnO is susceptible to other glazed roof tiles, the present invention does not contain ZnO and is sufficiently silvery. · _Al 2 _{O 3} even be possible with the · SiO ₂ to obtain the glaze tile unleaded glaze is less than 0.5 mol preferably 0.5 mol to 2.5 mol greater than 2.5 mol glaze foaming Is preferably 0.05 to 0.3, and if less than 0.05, soot foams. B ₂ O ₃ is an effective component for adjusting the viscosity of the soot and assisting the formation of crystals, but when the number of moles increases, The chemical durability of the cocoon Beat, discoloration by an acid is generated (omission) preferred molar ratio of a _· SiO 2 / _Al 2 _{O 3} in 0.05 to 0.18 mol is related to discoloration due to a molten state and acid glaze particular B Discoloration is significant when ₂ O ₃ is greater than 0.18 mol and the ratio of SiO ₂ / Al ₂ O ₃ is less than 4 • More stable against penetration by making R ₂ O 0.01 mol or less It can be made.

SrO, BaO, ZnO, MgO and CaO are defined in Patent Document 3 as 0.15 ≦ CaO ≦ 0.25 and RO ≦ 0.1 (RO: SrO, BaO, ZnO, MgO). In Patent Document 4, the requirement of 0.1 ≦ RO total amount ≦ 0.3 mol (RO: MgO, CaO, SrO and / or BaO) is indispensable. Not listed.
The reason why ZnO is not required in the invention described in Patent Document 3 is to prevent coloration inhibition by other color glazes under the current production situation of glaze tiles that simultaneously co-fire other color glazes by removing ZnO However, an indirect reason that it is possible to obtain stable color development is described.

As mentioned above, in the conventional silver lead-free glaze, MnO, ZrO ₂ and TiO ₂ , SiO ₂ and Al ₂ O ₃ , B ₂ O ₃ , R ₂ O (Li ₂ O, K ₂ O and / or Na ₂ O) ) And RO (SrO, BaO, MgO and / or CaO) are essential components and the required amounts for each component are also defined. ZnO may be an optional component.

JP 58-79838 A JP 58-88141 A JP 9-48682 A Japanese Patent Laid-Open No. 9-227153

In recent years, from the viewpoint of occupational health and environmental safety, there is a growing need for avoiding the use of silver lead-free glazes by adding components other than lead (and zinc).
However, each of the above-described components and their amounts described in Patent Document 3 are indispensable for silver-colored development, and silver-lead-free glaze excluding components other than lead is desired, but other than lead At present, the development and provision of silver-free lead-free glazes that exclude particularly harmful components has not yet begun.

  In view of the above problems, the present inventors have examined a silver-free lead glaze from which components other than lead are further removed, and surprisingly, the amount of some other components is adjusted without using certain components. As a result, the inventors have found that the above problem may be solved, and have made further researches. As a result, the present invention has been completed.

That is, the present invention provides R ¹ ₂ O (R ¹ ₂ O represents one or more of Li ₂ O, Na ₂ O and K ₂ O) in an amount of 0.06 mol ≧ R ¹ ₂ O;
0.05 mol ≦ CaO ≦ 0.34 mol of CaO;
Al ₂ O ₃ 0.02 mole ≦ _Al 2 _{O 3} ≦ 0.27 moles;
MnO relates to a silver-free lead-free glaze containing 0.65 mol ≦ MnO ≦ 0.95 mol; and TiO ₂ in an amount of 0.11 mol ≦ TiO ₂ and no boron.

The present invention, the SiO _2, about the silver leadless glaze further comprises an amount of 0.45 mole ≦ SiO ₂ ≦ 2.1 mol.
Furthermore, the present invention relates to the silver-free lead glaze further comprising R ² O (R ² O represents one or more of MgO, SrO and BaO) in an amount of 0.12 mol ≧ R ² O.
The present invention still further relates to the silver-free lead glaze that does not contain R ² O.
Furthermore, the present invention, the ZrO ₂ 0.54 mol ≧ _ZrO 2, further comprising in an amount of 0.74 mol ≧ _{ZrO 2} + TiO 2, relating to the one of silver lead-free glaze.
Furthermore, the present invention relates to any one of the above silver-free lead glazes not containing zinc.

The present invention also relates to a silver-free lead-free glaze containing no boron, comprising the following composition:
0.06 mol ≧ R ¹ ₂ O (R ¹ ₂ O represents one or more of Li ₂ O, Na ₂ O and K ₂ O);
0.05 mol ≦ CaO ≦ 0.34 mol;
0.12 mol ≧ R ² O (R ² O represents one or more of MgO, SrO and BaO)
0.45 mol ≦ SiO ₂ ≦ 2.1 mol;
Al ₂ O ₃ 0.02 mole ≦ _Al 2 _{O 3} ≦ 0.27 moles;
MnO 0.65 mol ≦ MnO ≦ 0.95 mol; and 0.54 mol ≧ ZrO ₂ , 0.11 mol ≦ TiO ₂ , 0.74 mol ≧ ZrO ₂ + TiO ₂ .

The present invention further relates to said silver-free lead glaze comprising the following composition:
0.06 mol ≧ R ¹ ₂ O (R ¹ ₂ O represents one or more of Li ₂ O, Na ₂ O and K ₂ O);
0.05 mol ≦ CaO ≦ 0.34 mol;
0.45 mol ≦ SiO ₂ ≦ 2.1 mol;
Al ₂ O ₃ 0.02 mole ≦ _Al 2 _{O 3} ≦ 0.27 moles;
MnO 0.65 mol ≦ MnO ≦ 0.95 mol; and 0.54 mol ≧ ZrO ₂ , 0.11 mol ≦ TiO ₂ , 0.74 mol ≧ ZrO ₂ + TiO ₂ .

  And this invention relates to the silver roof tile manufactured using the said any silver lead-free glaze.

According to the present invention, it is possible to provide a silver-free lead glaze from which boron is further removed as a component other than lead, thereby achieving further improvement in occupational health and environmental safety when producing a silver glaze and a silver roof tile.
The silver lead-free glaze of the present invention can sufficiently develop a silver color even though it does not contain boron.

The present invention has succeeded not only in avoiding the use of boron in silver-colored lead-free glazes, but also uses components such as R ¹ ₂ O, Al ₂ O ₃ , MnO and TiO ₂ in specific amounts to provide hygiene and environmental safety. This is significantly different from the prior art in that CaO, which is a component that does not have a major problem in this aspect, can be used in an amount larger than the conventional one. Considering that CaO has no major problems in terms of hygiene / environmental safety as described above, this is an exceptional effect that even a person skilled in the art can not imagine from the prior art.

While not wishing to be bound by theory, it is believed that CaO is a component that assists in the silver color development in silver-free lead glazes excluding B ₂ O ₃ .
In both Patent Documents 2 and 3, boron is considered to be indispensable as a component of the silver lead-free glaze. On the other hand, CaO is only a necessary component for smoothly melting glaze (silver-based lead-free glaze) together with B ₂ O ₃ and making it safe against penetration (Patent Document 2). In Patent Document 3 that discloses a silver-colored lead-free glaze that is considered to have good color stability, CaO is merely exemplified as one element of the RO component together with MgO, SrO, and BaO. No amount is stated. In other words, it has not been known at all that not only silver lead-free glazes that do not use B ₂ O ₃ at all, but also that such a glaze, CaO provides sufficient color development with the aid of silver color development.

Also those containing an additional amount of the amount of the SiO ₂ 0.45 mole ≦ SiO ₂ ≦ 2.1 mol of silver lead-free glazes of the present ^{invention, R 2} O (R 2 O is MgO, SrO and BaO of one or 2 or more) is contained in an amount of 0.12 mol ≧ R ² O, or ZrO ₂ is contained in an amount of 0.54 mol ≧ ZrO ₂ , 0.74 mol ≧ ZrO ₂ + TiO ₂ , It has the effect of preventing foaming and non-melting of the glaze on the surface and keeping the surface state good.

The present invention is described in further detail below. In addition, unless otherwise indicated, the amount of each component represents the number of moles in terms of Seegel.
The inventors first selected boron as what it would be desirable to remove from the components of conventional silver lead-free glazes. Boron is a component added to the wastewater standard as “boron and its compounds” by the revision of the Water Pollution Control Law of 2001.
On the other hand, boron is a component that plays an auxiliary role in the precipitation of crystals that promote melting of the glaze and become the element of silver color development. Therefore, for example, in the invention described in Patent Document 3, 0.05 to 0.18 mol of B ₂ O ₃ is considered indispensable. Also, an amount in the range of _B 2 _{O 3} in Patent Document 2 is 0.1 to 0.2 moles. That is, in the prior art, it is necessary to use at least 0.05 mol of boron (B ₂ O ₃ ).

If boron is not used, the glaze melts poorly and the fire resistance becomes high, and it becomes difficult to generate crystals of the elements (mainly Mn, other Zr, Ti, etc.) that cause silvery coloring, resulting in poor coloring and foaming. Undesirable phenomena can occur.
In order to suppress these undesirable phenomena, particularly coloring defects, it is effective to use components such as R ¹ ₂ O, Al ₂ O ₃ , MnO and TiO ₂ in specific amounts and adjust the amount of CaO. First discovered in the present invention. That is, by using specific components such as R ¹ ₂ O, Al ₂ O ₃ , MnO and TiO ₂ and using CaO in an amount that may be greater than that used in the prior art, the undesirable phenomenon is suppressed. It became clear that there is a tendency to be.

In the glaze of the present invention, R ¹ ₂ O (R ¹ ₂ O represents one or more of Li ₂ O, Na ₂ O and K ₂ O) in an amount of 0.06 mol ≧ R ¹ ₂ O Including. By using the R ¹ ₂ O in the above amount, not only silver color development is achieved, but also the melting point of the glaze is lowered and penetration is prevented.
0.06 mol ≧ ^R _{1 2} O ≧ 0.01 mole as the amount of R ¹ ₂ O Preferably, 0.05 mole ≧ ^R _{1 2} O ≧ 0.01 mol and more preferably, greater than 0.01 moles 0. An amount of 05 mol or less is even more preferred.

The glaze of the present invention contains 0.05 mol ≦ CaO ≦ 0.34 mol of CaO (0.05 mol or more and 0.34 mol or less. Hereinafter, the notation using “˜” in this specification has the same meaning). In the amount of. When the amount of CaO used is 0.05 mol or more, crystals of components such as MnO, which is a crystallizing agent that forms a silver color, are likely to be generated. The ratio can be kept appropriate, and the blackening of the tile using the glaze can be prevented.
The amount of CaO is preferably from 0.1 mol to 0.3 mol, more preferably from 0.15 mol to 0.3 mol, and even more preferably from 0.15 mol to 0.3 mol.

In the glaze of the present invention, Al ₂ O ₃ is contained in an amount of 0.02 mol ≦ Al ₂ O ₃ ≦ 0.27 mol. By using the Al ₂ O ₃ in the above-mentioned amount, not only silver color development is achieved, but also the surface condition can be improved.
The amount of Al ₂ O ₃ is preferably from 0.025 mol to 0.25 mol, more preferably from 0.03 mol to 0.25 mol, and even more preferably from 0.03 mol to 0.25 mol.

  In the glaze of the present invention, MnO is contained in an amount of 0.65 mol ≦ MnO ≦ 0.95 mol. The amount of MnO is preferably from 0.7 mol to 0.9 mol, more preferably from 0.75 mol to 0.9 mol, and even more preferably from 0.75 mol to 0.9 mol.

Glazes of the present invention comprises TiO ₂ in an amount of 0.11 mole ≦ TiO _2. TiO ₂ is a component that promotes the precipitation of silvery component crystals, like ZrO ₂ .
Those containing an amount of TiO ₂ 0.11 mole ≦ TiO ₂ ≦ 0.5 moles of glaze of the present invention is preferably, and more preferably those containing in an amount of 0.15 mole ≦ ZrO ₂ ≦ 0.5 mol, An amount greater than 0.15 mol and less than 0.5 mol is even more preferred.
Although the amount of TiO ₂ is relatively larger than that in the prior art, the amount can supplement the effect of assisting the precipitation of boron crystals.

Also, the glaze of the present invention where it is intended to include SiO _2, the amount but is not limited those more preferred in an amount of SiO ₂ 0.45 mole ≦ SiO ₂ ≦ 2.1 mol. These amounts are relatively small compared to the amounts in the prior art, and contribute to more stable color development and prevention of foaming in the boron-free silver-colored lead-free glaze of the present invention.
Those containing an amount of the SiO ₂ 0.5 moles ≦ SiO ₂ ≦ 2.1 moles of glaze of the present invention is preferably, and more preferably those containing in an amount of 0.5 mole ≦ SiO ₂ ≦ 2.0 mol, An amount of more than 0.5 mol and not more than 2.0 mol is even more preferable.

The other components contained in the silver lead-free glaze of the present invention will be described below.
The glaze of the present invention may contain R ² O (R ² O represents one or more of MgO, SrO and BaO, the same shall apply hereinafter), and the amount of R ² O is 0.12 mol ≧ R ² O Including is preferable. By making the amount of R ² O 0.12 mol or less, melting and color development of the glaze can be further stabilized.
More preferably those containing in an amount of 0.1 mol ≧ ^{R 2} O mole ^{R 2} O of glaze of the present invention, even more preferably those containing in an amount of 0.075 mol ≧ ^{R 2,} less than 0.075 moles The amount of is even more preferred. Also preferred are glazes according to the invention which do not contain R ² O.

Of the glazes of the present invention, those containing ZrO ₂ are preferred, and those containing ZrO ₂ in amounts of 0.54 mol ≧ ZrO ₂ and 0.74 mol ≧ ZrO ₂ + TiO ₂ are more preferred. ZrO ₂ is a component that promotes the precipitation of silvery component crystals, like TiO ₂ . What is more preferably in an amount of ZrO ₂ 0.1 mole ≦ ZrO ₂ ≦ 0.54 moles of glaze of the present invention, even more is intended to include an amount of 0.1 mole ≦ ZrO ₂ ≦ 0.5 mol Preferably, an amount greater than 0.1 mole and less than or equal to 0.5 mole is even more preferred.
By making the addition amount of ZrO ₂ 0.54 mol or less, the influence of its extremely high fire resistance can be appropriately suppressed. Further by 0.74 mol ≧ _{ZrO 2} + TiO 2, it is possible to maintain the molten state of the glaze better. Of the glazes of the present invention, those having 0.74 mol ≧ ZrO ₂ + TiO ₂ ≧ 0.1 mol are more preferred, those having 0.7 mol ≧ ZrO ₂ + TiO ₂ ≧ 0.1 mol are even more preferred, and ZrO It is even more preferable that ₂ + TiO ₂ is greater than 0.1 mole and less than or equal to 0.7 mole.

Of the glazes of the present invention, those not containing zinc (ZnO) are also preferred. By avoiding the use of ZnO, in the current production situation of glaze tiles that co-fire not only silver glaze but also other color glazes, to prevent color inhibition by other color glazes and achieve more stable color development Can do.
Among the glazes of the present invention that do not contain zinc, the preferred additions and / or amounts of the above components are also applied. However, the glaze of the present invention contains R ¹ ₂ O (R ¹ ₂ O represents one or more of Li ₂ O, Na ₂ O and K ₂ O) in an amount of 0.06 mol ≧ R ¹ ₂ O; CaO 0.05 mol ≦ CaO ≦ 0.34 mol; Al ₂ O ₃ 0.02 mol ≦ Al ₂ O ₃ ≦ 0.27 mol; MnO 0.65 mol ≦ MnO ≦ 0.95 mol; and TiO ₂ As long as it is a silver lead-free glaze that contains 0.11 mol ≦ TiO ₂ and does not contain boron, the types and amounts of the other components are not particularly limited. Therefore, the silver lead-free glaze of the present invention may contain zinc as appropriate.

Of the silver-free lead glazes of the present invention, those containing no boron and having the following composition are particularly preferred:
0.06 mol ≧ R ¹ ₂ O (R ¹ ₂ O represents one or more of Li ₂ O, Na ₂ O and K ₂ O);
0.05 mol ≦ CaO ≦ 0.34 mol;
0.12 mol ≧ R ² O (R ² O represents one or more of MgO, SrO and BaO)
0.45 mol ≦ SiO ₂ ≦ 2.1 mol;
Al ₂ O ₃ 0.02 mole ≦ _Al 2 _{O 3} ≦ 0.27 moles;
MnO 0.65 mol ≦ MnO ≦ 0.95 mol; and 0.54 mol ≧ ZrO ₂ , 0.11 mol ≦ TiO ₂ , 0.74 mol ≧ ZrO ₂ + TiO ₂ .

Among the above silver lead-free glazes of the present invention, those having the following composition are more particularly preferred because they do not contain R ² O:
0.06 mol ≧ R ¹ ₂ O (R ¹ ₂ O represents one or more of Li ₂ O, Na ₂ O and K ₂ O);
0.05 mol ≦ CaO ≦ 0.34 mol;
0.45 mol ≦ SiO ₂ ≦ 2.1 mol;
Al ₂ O ₃ 0.02 mole ≦ _Al 2 _{O 3} ≦ 0.27 moles;
MnO 0.65 mol ≦ MnO ≦ 0.95 mol; and 0.54 mol ≧ ZrO ₂ , 0.11 mol ≦ TiO ₂ , 0.74 mol ≧ ZrO ₂ + TiO ₂ .

  The silver-colored lead-free glaze of the present invention can be produced by a conventional method. For example, what is necessary is just to prepare the formulation of a desired composition using raw materials, such as a quartzite, a kaolin, a glazed clay, manganese oxide, a rutile, iron oxide. Further, an appropriate amount of additives such as CMC and bentonite may be added thereto, and wet milling may be performed with a pot mill or the like to obtain a final preparation.

The present invention also relates to a silver roof tile manufactured using any one of the above silver lead-free glazes, and the roof tile can be manufactured by a usual method in this technical field. That is, the firing temperature of the roof tile can be about 1100 ° C. to about 1160 ° C., and the amount of glazed deposit can be 50 g to 90 g / Japanese-style roof tile.
In addition, the silver-free lead glaze of the present invention may contain components other than those described above as components that inevitably mix the effects of the silver-lead-free glaze in the course of the manufacturing process, as long as the object of the present invention is not impaired. .

  Hereinafter, the present invention will be described in more detail by way of specific examples, but this does not limit the present invention in any way.

Example 1
[Test method]
Prepare a composition having the composition shown in each example of Table 1 using raw materials such as silica, kaolin, cocoon clay, manganese oxide, rutile, iron oxide, etc., and add 0.5 parts each of CMC and bentonite to the pot mill. The wet crushed material was glazed so as to give an adhesion amount of 80 to 90 g per sheet of Japanese type roof tile, and fired at the temperatures shown in Table 1 to obtain tiles. In addition, the said temperature considered the composition of each glaze, and set the thing which makes the coloring and glazing state which should become silver color as appropriate as possible.

The color development of the obtained roof tile was judged by visual observation.
Further, the surface condition was visually observed from the degree of melting of the glaze and the presence or absence of foaming.

[result]
The results are shown in Table 1.

All of the glazes of the present invention (Examples 1 to 22) developed a silver color.
In contrast, Comparative Examples 1 to 4 have R ¹ ₂ O (Comparative Example 1), CaO and MnO (Comparative Example 2), Al ₂ O ₃ (Comparative Example 3) and TiO ₂ (Comparative Example 4), respectively. In these examples, the color of the roof tiles was black and silver color development was not achieved.
In addition, in Examples 1-16 among Examples 1-22, the ridge surface state was especially favorable.

According to the method of the present invention, it is possible to provide a silver-free lead glaze excluding components other than lead. Therefore, the present invention greatly contributes to the development of the glaze manufacturing industry, the silver tile manufacturing industry and related industries.

Claims (9)

In terms of Seegel, R ¹ ₂ O (R ¹ ₂ O represents one or more of Li ₂ O, Na ₂ O and K ₂ O) is 0.06 mol ≧ R ¹ ₂ O ≧ 0.025 mol ;
0.05 mol ≦ CaO ≦ 0.34 mol of CaO;
Al ₂ O ₃ 0.02 mole ≦ _Al 2 _{O 3} ≦ 0.27 moles;
A silver-free lead-free glaze containing MnO in an amount of 0.65 mol ≦ MnO ≦ 0.95 mol; and TiO ₂ in an amount of 0.11 mol ≦ TiO ₂ and no boron. The SiO ₂ further comprising in an amount of 0.45 mole ≦ SiO ₂ ≦ 2.1 mol, silver leadless glaze of claim 1. ^3. The silver-free lead glaze according to claim 1, further comprising R ² O (R ² O represents one or more of MgO, SrO, and BaO) in an amount of 0.12 mol ≧ R ² O. 4. The ZrO ₂ 0.54 mol ≧ _ZrO 2, further comprising in an amount of 0.74 mol ≧ _{ZrO 2} + TiO 2, silver leadless glaze as claimed in any one of claims 1-3. The silver-free lead-free glaze according to any one of claims 1 to 4 , which does not contain zinc. A silver-free lead-free glaze containing no boron and consisting of the following composition:
0.06 mol ≧ R ¹ ₂ O ≧ 0.025 mol (R ¹ ₂ O represents one or more of Li ₂ O, Na ₂ O and K ₂ O);
0.05 mol ≦ CaO ≦ 0.34 mol;
0.12 mol ≧ R ² O (R ² O represents one or more of MgO, SrO and BaO)
0.45 mol ≦ SiO ₂ ≦ 2.1 mol;
Al ₂ O ₃ 0.02 mole ≦ _Al 2 _{O 3} ≦ 0.27 moles;
MnO 0.65 mol ≦ MnO ≦ 0.95 mol; and 0.54 mol ≧ ZrO ₂ , 0.11 mol ≦ TiO ₂ , 0.74 mol ≧ ZrO ₂ + TiO ₂ . The silver-free lead-free glaze according to claim 6 comprising the following composition:
0.06 mol ≧ R ¹ ₂ O ≧ 0.025 mol (R ¹ ₂ O represents one or more of Li ₂ O, Na ₂ O and K ₂ O);
0.05 mol ≦ CaO ≦ 0.34 mol;
0.45 mol ≦ SiO ₂ ≦ 2.1 mol;
Al ₂ O ₃ 0.02 mole ≦ _Al 2 _{O 3} ≦ 0.27 moles;
MnO 0.65 mol ≦ MnO ≦ 0.95 mol; and 0.54 mol ≧ ZrO ₂ , 0.11 mol ≦ TiO ₂ , 0.74 mol ≧ ZrO ₂ + TiO ₂ . A method for producing a silver roof tile, comprising: applying a silver lead-free glaze according to any one of claims 1 to 7 to a roof tile, and firing the roof tile to develop a silver color. Silver tiles produced using the silver lead-free glaze according to any of claims 1-7.