'Shengshan' cobalt material for imitated early blue and white porcelain, preparation method of 'Shengshan' cobalt material, imitated early blue and white porcelain and preparation method of imitated early blue and white porcelain

Abstract

The invention relates to the technical field of inorganic non-metallic materials, in particular to a'halo powder 'cobalt material for imitated early blue and white porcelain, a preparation method of the'halo powder' cobalt material, the imitated early blue and white porcelain and a preparation method of the imitated early blue and white porcelain. The preparation method of the'halo powder 'cobalt material for the imitated early blue and white porcelain of the Mingming generation comprises the following steps: A) grinding raw materials to obtain mixed powder; wherein the raw materials comprise the following components in parts by mass: 5-20 parts of a chemical pure cobalt material; 40 to 60 parts of quartz; 40 to 60 parts of borax; 40-60 parts of plant ash; 0-15 parts of iron oxide; and B) carrying out heat treatment on the mixed powder obtained in the step A) to obtain the blue-and-white cobalt material. The'halo 'cobalt material provided by the invention can improve the color generation and halo effect, achieves the iron rusty spot effect, and has the characteristics of blue and white porcelains of the official kilns in the early stage of Ming.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic non-metallic materials, and in particular to a "diffuse" cobalt material used for imitating early Ming Dynasty blue-and-white porcelain and a preparation method thereof, and imitating early Ming Dynasty blue-and-white porcelain and a preparation method thereof. Background Art

[0002] Early Ming blue-and-white porcelain (Hongwu to Xuande) was in the transition period between Yuan and Ming, and played an important role in connecting the past and the future. Ancient ceramics research experts such as Feng Xianming and Geng Baochang pointed out that the early Ming blue-and-white porcelain was influenced by the culture of West Asia in terms of shape and decoration. Not limited to shape and decoration, an important identification feature of early Ming blue-and-white porcelain is the use of an imported cobalt material called "Sumaliqing", and the blue-and-white decoration has a halo phenomenon, and the lines drawn by the cobalt material are unclear and uneven. The characteristics of blue-and-white porcelain from the mid-Ming Dynasty to the Qing Dynasty are clear strokes, distinct layers of decoration, and clear boundaries. At present, most imitations of early Ming blue-and-white porcelain directly use chemical cobalt materials, which cannot fully reproduce the color and halo effect of early Ming blue-and-white porcelain. Summary of the invention

[0003] In view of this, the present invention provides a "diffuse" cobalt material used for imitating early Ming Dynasty blue-and-white porcelain and a preparation method thereof, and an imitation Ming Dynasty early blue-and-white porcelain and a preparation method thereof. The "diffuse" cobalt material provided by the present invention can improve the coloring and diffusing effects, and achieve the effect of rust spots.

[0004] The present invention provides a method for preparing a "dispersed" cobalt material used in imitation of early Ming Dynasty blue and white porcelain, comprising the following steps:

[0005] A) grinding the raw materials to obtain a mixed powder;

[0006] Wherein, in parts by mass, the raw materials include:

[0007]

[0008] B) heat-treating the mixed powder obtained in step A) to obtain blue and white cobalt material.

[0009] Preferably, in step B), the heat treatment conditions are as follows: firstly heating to 600°C, and then heating to 1050-1150°C and keeping warm.

[0010] Preferably, in step B), the heat treatment conditions are as follows: firstly heating to 600°C at a heating rate of 5-10°C / min and keeping warm for 0.0-0.5h, then heating to 1050-1150°C at a heating rate of 5-10°C / min and keeping warm for 0.5-2h.

[0011] Preferably, in step B), after the heat treatment, crushing and grinding are further performed to control the particle size of the material to be 80-200 meshes.

[0012] Preferably, in step A), the grinding is ball milling;

[0013] The ball milling medium used in the ball milling is water;

[0014] In the ball milling, the weight ratio of raw material: ball mill stone: ball mill medium is 1: (1.0-1.2): (1.0-1.2);

[0015] The ball mill has a rotation speed of 300 to 350 r / min and a time of 5 to 30 min.

[0016] The present invention also provides a "dispersed" cobalt material used for imitating blue-and-white porcelain of the early Ming Dynasty, which is prepared by the preparation method described in the above technical solution.

[0017] The present invention also provides an imitation Ming Dynasty early blue-and-white porcelain, the drawing material adopted by the imitation Ming Dynasty early blue-and-white porcelain is the "diffuse" cobalt material used in the above technical solution.

[0018] The present invention also provides a method for preparing the blue-and-white porcelain imitating the early Ming Dynasty described in the above technical solution, comprising: drawing a drawing material on a blank, then glazing and sintering to obtain a blue-and-white porcelain product;

[0019] Wherein, the drawing material is the "diffuse" cobalt material used for imitating the early blue and white porcelain of the Ming Dynasty as described in the above technical solution.

[0020] Preferably, the sintering includes: first heating the temperature to 600° C., and then heating the temperature to 1180-1300° C. and maintaining the temperature.

[0021] Preferably, the sintering comprises: firstly heating the temperature to 600°C at a heating rate of 5-10°C / min and keeping the temperature for 0.0-0.5h, then heating the temperature to 1180-1300°C at a heating rate of 5-10°C / min and keeping the temperature for 0.5-2h;

[0022] The sintering is carried out in a high temperature electric furnace under an oxidizing atmosphere or in a gas furnace under a reducing atmosphere.

[0023] The "diffuse" cobalt material provided by the present invention is prepared by mixing chemical pure cobalt material, quartz, borax, plant ash and iron oxide in a certain proportion as raw materials, crushing and subjecting the raw materials to high-temperature treatment under certain conditions to obtain cobalt blue glass material with high silicon and high boron; wherein, by adjusting the proportion of the raw materials, the sintering reaction can be more thorough, and the coloring and diffusing effects can be better; after high-temperature calcination, the material is crushed and ground to control a certain particle size so that the drawn blue and white porcelain has an iron rust spot effect; and the material has the characteristics of blue and white porcelain from the official kiln of the early Ming Dynasty. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1 This is a physical picture of the blue and white porcelain product obtained in Example 1;

[0026] Figure 2 This is a physical picture of the blue and white porcelain product obtained in Example 2;

[0027] Figure 3 This is a physical picture of the blue and white porcelain product obtained in Example 3. DETAILED DESCRIPTION

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0029] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0030] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0031] Herein, when it comes to numerical ranges, unless otherwise specified, the numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0032] In this article, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 300-350r / min means that the units of the left endpoint "300" and the right endpoint "350" are both r / min.

[0033] The present invention provides a method for preparing a "dispersed" cobalt material used in imitation of early Ming Dynasty blue and white porcelain, comprising the following steps:

[0034] A) grinding the raw materials to obtain a mixed powder;

[0035] Wherein, in parts by mass, the raw materials include:

[0036]

[0037] B) heat-treating the mixed powder obtained in step A) to obtain blue and white cobalt material.

[0038] [About Step A]:

[0039] In the present invention, the raw materials include, by weight:

[0040]

[0041] in:

[0042] The purity of the chemical pure cobalt material (i.e., cobalt single substance raw material, Co) is preferably ≥99%, and its source is not particularly limited, and it can be a commercial product, for example, it can be from Sinopharm Group, Wokai Company, etc. The amount of the chemical pure cobalt material can be 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts.

[0043] The amount of quartz used may specifically be 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, and 60 parts.

[0044] The specific amount of borax used can be 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, and 60 parts.

[0045] The specific amount of the wood ash may be 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts, and 60 parts.

[0046] The content of the iron oxide can specifically be 0 parts, 1 parts, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, and 15 parts.

[0047] In the present invention, the preferred method for grinding the above raw materials is ball milling. In the present invention, the ball milling medium used in the ball milling is preferably water. In the ball milling, the weight ratio of raw material: ball mill stone: ball milling medium is preferably 1: (1.0-1.2): (1.0-1.2), more preferably 1: 1: 1. In the present invention, the rotation speed of the ball milling is preferably 300-350 r / min, specifically 300 r / min, 310 r / min, 320 r / min, 330 r / min, 340 r / min, 350 r / min; the ball milling time is preferably 5-30 min, specifically 5 min, 10 min, 15 min, 20 min, 25 min, 30 min.

[0048] In the present invention, after ball milling, a slurry is obtained. In the present invention, the slurry is preferably dried. The drying may be natural drying or oven drying. After drying, a uniformly mixed powder is obtained.

[0049] [About step B]:

[0050] In the present invention, after the mixed powder is obtained in step A), heat treatment is performed. In the present invention, the heat treatment is preferably a multi-stage heating treatment. More preferably, the heat treatment includes: first heating to 600°C, then heating to 1050-1150°C and keeping warm.

[0051] in,

[0052] The heating rate to 600°C is preferably 5-10°C / min, specifically 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min. The holding time after heating to 600°C is preferably 0.0-0.5h, specifically 0.0h, 0.1h, 0.2h, 0.3h, 0.4h, 0.5h.

[0053] The heating rate to 1050-1150°C is preferably 5-10°C / min, specifically 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min. The target temperature of the heating can be specifically 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C. The holding time after heating to 1050-1150°C is preferably 0.5-2h, specifically 0.5h, 1h, 1.5h, 2h.

[0054] In the present invention, after the above heat treatment, the cobalt glass material is naturally cooled with the furnace to obtain a cobalt material glass material. In the present invention, after obtaining the cobalt material glass material, secondary crushing and grinding treatment are also carried out. Among them, the grinding treatment can be specifically ground with an agate mortar, and the grinding time is preferably 0.5 to 2.0 hours. After the above treatment, the material particle size is controlled to be 80 to 200 mesh, specifically 80 mesh, 90 mesh, 100 mesh, 110 mesh, 120 mesh, 130 mesh, 140 mesh, 150 mesh, 160 mesh, 170 mesh, 180 mesh, 190 mesh, 200 mesh. After the above treatment, a blue and white cobalt material with a dizzy effect is obtained.

[0055] The present invention also provides a "dispersed" cobalt material used for imitating blue-and-white porcelain of the early Ming Dynasty, which is prepared by the preparation method described in the above technical solution.

[0056] The preparation method of the present invention can stably synthesize a "diffuse" cobalt material with stable coloring used in imitation of early Ming Dynasty blue and white porcelain, which is similar to the coloring and diffusing effect of early Ming Dynasty official kiln blue and white porcelain. Moreover, the preparation process of the blue and white material of the present invention is simple and clear, easy to control, and has good stability, and has good industrial application value and prospects.

[0057] The present invention also provides an imitation Ming Dynasty early blue-and-white porcelain, the drawing material adopted by the imitation Ming Dynasty early blue-and-white porcelain is the "diffuse" cobalt material used in the above technical solution.

[0058] The present invention also provides a preparation method of imitation Ming Dynasty early blue-and-white porcelain, comprising: drawing a drawing material on a blank, then glazing and sintering to obtain a blue-and-white porcelain product; wherein the drawing material is the "diffuse" cobalt material used for imitation Ming Dynasty early blue-and-white porcelain described in the above technical solution.

[0059] in,

[0060] The drawing material is drawn on the blank to form a blue and white decoration. The glazing treatment method is not particularly limited, and it can be a conventional method in the field, such as dipping glaze method, brushing glaze method, spraying glaze method, etc. The glaze used is not particularly limited, and it can be a conventional transparent glaze in the field. After the glazing treatment, it is preferably dried.

[0061] The sintering process is preferably a multi-stage sintering process. More preferably, the sintering process includes: first heating to 600°C, then heating to 1180-1300°C and maintaining the temperature.

[0062] in,

[0063] The heating rate to 600°C is preferably 5-10°C / min, specifically 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min. The holding time after heating to 600°C is preferably 0.0-0.5h, specifically 0.0h, 0.1h, 0.2h, 0.3h, 0.4h, 0.5h.

[0064] The heating rate to 1180-1300°C is preferably 5-10°C / min, specifically 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min. The target temperature of the heating can be specifically 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C, 1250°C, 1260°C, 1270°C, 1275°C, 1280°C, 1290°C, 1300°C. The holding time after heating to 1180-1300°C is preferably 0.5-2h, specifically 0.5h, 1h, 1.5h, 2h.

[0065] The sintering can be carried out in a high-temperature electric furnace or a gas furnace. Among them, the high-temperature electric furnace sintering is sintering in an oxidizing atmosphere. The gas furnace sintering is sintering in a reducing atmosphere. In the present invention, after the above sintering treatment, the blue and white porcelain product is obtained by natural cooling along with the furnace.

[0066] The "diffuse" cobalt material provided by the present invention is prepared by mixing chemical pure cobalt material, quartz, borax, plant ash and iron oxide in a certain proportion as raw materials, crushing and subjecting the raw materials to high-temperature treatment under certain conditions to obtain cobalt blue glass material with high silicon and high boron; wherein, by adjusting the proportion of the raw materials, the sintering reaction can be more thorough, and the coloring and diffusing effects can be better; and after high-temperature calcination, the material is crushed and ground to control a certain particle size so that the drawn blue and white porcelain has a rust spot effect.

[0067] The invention provides a preparation method for imitation blue-and-white porcelain of the early Ming Dynasty, which adopts the above-mentioned "diffuse" cobalt material as a drawing material to draw patterns on a blue-and-white porcelain blank, and then performs glazing treatment and high-temperature sintering treatment, wherein the cobalt material is fired under an oxidizing atmosphere in a high-temperature electric furnace and under a reducing atmosphere in a gas furnace, and has the effects of stable color, diffusiveness and rust spots, achieving a color effect similar to that of blue-and-white porcelain of the early Ming Dynasty.

[0068] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0069] Example 1

[0070] 1. Preparation of "dispersed" cobalt material

[0071] A) The raw materials were put into a ball mill, and the weight ratio of raw materials: ball mill stone: water was 1:1:1, and the ball mill was operated at 300 r / min for 10 minutes to obtain a slurry. Then, the slurry was dried to obtain a mixed powder.

[0072] Among them, the raw material composition is as follows:

[0073]

[0074] B) Place the mixed powder in a refractory crucible and perform a melting process in a high-temperature electric furnace. Specifically, heat the mixture to 600°C at 10°C / min and keep it for 0.1h, then heat the mixture to 1150°C at 10°C / min and keep it for 0.5h; then cool it naturally in the furnace to obtain a cobalt glass. Perform secondary crushing and grinding on the obtained cobalt glass, and pass it through a 100-mesh sieve to obtain a blue-and-white cobalt material.

[0075] 2. Preparation of blue and white porcelain

[0076] The obtained blue and white cobalt material is painted on the blank, then glazed and dried. After that, it is sintered in a high-temperature electric furnace in an oxidizing atmosphere under the following conditions: first, the temperature is raised to 600℃ at 10℃ / min and kept at this temperature for 0.1h, then the temperature is raised to 1225℃ at 10℃ / min and kept at this temperature for 0.5h; then, it is naturally cooled with the furnace to obtain an imitation of the early Ming Dynasty blue and white porcelain product.

[0077] The obtained product is Figure 1 As shown, it can be seen that the blue and white material has stable color, elegant color, and rust spots, which are the characteristics of blue and white porcelain from the official kilns of the early Ming Dynasty.

[0078] Example 2

[0079] 1. Preparation of "dispersed" cobalt material

[0080] A) The raw materials were put into a ball mill, and the weight ratio of raw materials: ball mill stone: water was 1:1:1, and the ball mill was operated at 300 r / min for 10 minutes to obtain a slurry. Then, the slurry was dried to obtain a mixed powder.

[0081] Among them, the raw material composition is as follows:

[0082]

[0083] B) Place the mixed powder in a refractory crucible and perform a melting process in a high-temperature electric furnace. Specifically, heat the mixture to 600°C at 10°C / min and keep it for 0.2h, then heat the mixture to 1150°C at 10°C / min and keep it for 0.5h; then cool it naturally in the furnace to obtain a cobalt glass. Perform secondary crushing and grinding on the obtained cobalt glass, and pass it through a 100-mesh sieve to obtain a blue-and-white cobalt material.

[0084] 2. Preparation of blue and white porcelain

[0085] The obtained blue and white cobalt material is painted on the blank, then glazed and dried. After that, it is sintered in a gas furnace under a reducing atmosphere under the following conditions: first, the temperature is raised to 600℃ at 10℃ / min and kept at this temperature for 0.2h, then the temperature is raised to 1275℃ at 10℃ / min and kept at this temperature for 0.5h; then, it is cooled naturally in the furnace to obtain an imitation of the early Ming Dynasty blue and white porcelain product.

[0086] The obtained product is Figure 2 As shown, it can be seen that the blue and white material has bright and gorgeous color with a halo phenomenon, which is the characteristic of blue and white porcelain from the official kilns of the early Ming Dynasty.

[0087] Example 3

[0088] 1. Preparation of "dispersed" cobalt material

[0089] A) The raw materials were placed in a ball mill, with the weight ratio of raw materials: ball mill stone: water being 1:1:1, and ball milled at 350 r / min for 10 min to obtain a slurry. The slurry was then dried to obtain a mixed powder.

[0090] Among them, the raw material composition is as follows:

[0091]

[0092] B) Place the mixed powder in a refractory crucible and perform a melting process in a high-temperature electric furnace. Specifically, heat the mixture to 600°C at 10°C / min and keep it for 0.3h, then heat the mixture to 1150°C at 10°C / min and keep it for 0.5h; then cool it naturally in the furnace to obtain a cobalt glass. Perform secondary crushing and grinding on the obtained cobalt glass, and pass it through a 100-mesh sieve to obtain a blue-and-white cobalt material.

[0093] 2. Preparation of blue and white porcelain

[0094] The obtained blue and white cobalt material is painted on the blank, then glazed and dried. After that, it is sintered in a high-temperature electric furnace in an oxidizing atmosphere under the following conditions: first, the temperature is raised to 600°C at 10°C / min and kept at this temperature for 0.3h, then the temperature is raised to 1230°C at 10°C / min and kept at this temperature for 1.5h; then, it is naturally cooled in the furnace to obtain an imitation of the early Ming Dynasty blue and white porcelain product.

[0095] The obtained product is Figure 3 As shown, it can be seen that the blue and white material has an elegant color and rust spots, which is the characteristic of blue and white porcelain from the official kilns of the early Ming Dynasty.

[0096] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for preparing a "dispersed" cobalt material used in imitation of early Ming Dynasty blue and white porcelain, characterized in that: The following steps are involved: A) grinding the raw materials to obtain a mixed powder; Wherein, in parts by mass, the raw materials include: B) heat-treating the mixed powder obtained in step A) to obtain blue and white cobalt material.

2. The preparation method according to claim 1, characterized in that: In step B), the heat treatment conditions are as follows: firstly heating to 600°C, and then heating to 1050-1150°C and keeping warm.

3. The preparation method according to claim 1 or 2, characterized in that: In step B), the heat treatment conditions are as follows: firstly, the temperature is increased to 600°C at a heating rate of 5-10°C / min and kept at that temperature for 0.0-0.5h, and then the temperature is increased to 1050-1150°C at a heating rate of 5-10°C / min and kept at that temperature for 0.5-2h.

4. The preparation method according to claim 1, characterized in that: In step B), after the heat treatment, the material is crushed and ground to control the particle size of the material to be 80-200 meshes.

5. The preparation method according to claim 1, characterized in that: In step A), the grinding is ball milling; The ball milling medium used in the ball milling is water; In the ball milling, the weight ratio of raw material: ball mill stone: ball mill medium is 1: (1.0-1.2): (1.0-1.2); The ball mill has a rotation speed of 300 to 350 r / min and a time of 5 to 30 min.

6. A "diffuse" cobalt material imitating the blue and white porcelain used in the early Ming Dynasty, characterized in that: The method is prepared according to any one of claims 1 to 5.

7. An imitation of early Ming Dynasty blue and white porcelain, characterized in that: The drawing material used is the "diffuse" cobalt material used for imitating the early Ming Dynasty blue and white porcelain as described in claim 6.

8. A method for preparing the imitation early Ming Dynasty blue and white porcelain according to claim 7, characterized in that: include: Drawing the drawing material on the blank, then glazing and sintering to obtain a blue and white porcelain product; Wherein, the drawing material is the "diffuse" cobalt material used for imitating the early Ming Dynasty blue and white porcelain as described in claim 6.

9. The preparation method according to claim 8, characterized in that: The sintering comprises: firstly heating the temperature to 600° C., and then heating the temperature to 1180-1300° C. and keeping the temperature.

10. The preparation method according to claim 8 or 9, characterized in that: The sintering comprises: firstly heating the temperature to 600°C at a heating rate of 5-10°C / min and keeping the temperature for 0.0-0.5h, then heating the temperature to 1180-1300°C at a heating rate of 5-10°C / min and keeping the temperature for 0.5-2h; The sintering is carried out in a high temperature electric furnace under an oxidizing atmosphere or in a gas furnace under a reducing atmosphere.

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