JP5488055B2 - Method for producing noble metal article - Google Patents

Description

  The present invention relates to a method for producing a noble metal article in which a gold coating layer is formed on at least a part of the surface of a silver clay sintered body.

Silver clay is a material that combines plastic powder with organic binders to give plasticity, so that it can be made by hand to make a silver shaped article, and when sintered, a silver shaped article is obtained, a hobby material, It is known as a jewelry material (see Patent Document 1).
Silver clay includes clay-like, paste-like, sheet-like ones that contain water, and blocks and plate-like shapes that have been molded and dried for engraving plates before sintering. And in the form of a pre-sintered molded intermediate that has been shaped into a ring shape, star shape, heart shape, cross shape, character shape, etc. and dried.
There is a desire to color part or all of a work (silver viscosity work) produced by shaping and sintering such silver clay. In particular, there is a desire to color gold and gold to give a high-class feel.

As a means to color such silver clay works by hand, it is soaked in an smoldering solution to sulfidize the surface, blacken the glass by cloisonne, emerald or ruby using silver clay sintering shrinkage, etc. There are methods for fitting colored solids.
In addition, as a method of coloring gold with golden color, a method of coating gold foil or gold foil in the form of crushed flakes, a gold paste prepared by combining gold powder and organic binders and applying it to silver clay works And a method of electroplating gold with a simple plating tool (for example, “Plating Kobo” manufactured by Marui Metal Industry Co., Ltd.) and a method of applying a colloidal gold solution having the property of sintering at room temperature. .

  When covering gold foil or gold leaf with crushed flake-like gold powder, the adhesion to the silver clay works as a base material cannot be sufficiently secured, and it is rubbed by touching with a daily hand such as a ring, pendant or earring. It cannot be used for works that are used in various ways. It is possible to increase the adhesion by heat treatment, but if you heat a silver clay piece covered with gold flakes or flaky gold powder that has been pulverized, the gold will turn up in some places. There are problems such as exposure of silver.

  Depending on the particle size of the gold powder, when applying gold paste to a silver clay piece and baking it, it is necessary to polish the gold powder after it has been sintered together in order to develop a brilliant golden color. However, it is necessary to heat it as 500 degreeC or more as baking temperature. However, since the alloying of gold and silver starts at about 200 ° C., when the alloy is heated to 500 ° C. or higher, the alloying of gold and silver proceeds, and the color becomes silver. In order to avoid this and obtain a golden color, it is necessary to apply gold paste repeatedly to a thickness of 100 μm or more. Therefore, there is a problem that the amount of gold used increases.

When gold is electroplated with a simple plating tool, the amount of gold used can be reduced because it can be thinly and uniformly coated to a thickness of 0.02 μm to 0.2 μm per time. However, it is known that gold is worn at a thickness of about 1 μm per year when worn as a decoration. For this reason, it is used in harsh environments such as rings that can be worn daily, touched by hand, immersed in water, washed with soap or household detergent, or wiped with a towel. As a result, there is a problem that the color fading occurs in a shorter time. In order to prevent this, it is necessary to plate to a thickness of at least 0.2 μm, desirably 1 μm or more.
However, when the silver clay sintered body is plated with gold, since the silver clay sintered body is porous, there is a problem that pinholes are likely to occur as compared with a silver melt produced by the lost wax method. Silver products are susceptible to the sulfidation of the silver of the base material, and if there is a pinhole, the silver at that part is sulfidized and black spots such as spots are generated, which is not preferable. In particular, since the silver clay sintered body is porous and the pores communicate with each other, if there is a pinhole, there is a tendency that sulfidation proceeds not only in the pinhole portion but also in the periphery. In order to prevent this, it is conceivable to perform nickel base plating. However, since nickel has an allergic reaction, it is not preferable for use on a body such as a ring. Therefore, when gold is electroplated with a simple plating tool or the like, a surface treatment method that is suitable for a silver clay sintered body and hardly generates sulfur is required.

  When applying a room temperature-sinterable gold colloid solution as disclosed in Patent Document 2, the thickness is 0.05 μm to 0.5 μm per time as in the case of electroplating gold with a simple plating tool. Since gold can be thinly and uniformly coated, the amount of gold used can be reduced. Moreover, there is a feature that it is difficult to make a pinhole. However, the adhesiveness is weaker than electroplating, and in particular, there is a problem that it is easy to peel off when formed directly on a mirror-polished silver clay sintered body with a thickness of 1 μm or more. Therefore, when applying a room temperature-sinterable gold colloid solution, a base treatment method that is suitable for a silver clay sintered body and difficult to peel off is required.

Japanese Patent Laid-Open No. 2002-241802 Japanese Patent No. 4282630

  The present invention has been made in view of such circumstances, and silver sulfidation hardly occurs, and even in a harsh usage environment such as a ring, the golden shine is maintained over a long period of time. It is an object of the present invention to provide a method for producing a noble metal article that hardly causes delamination.

The present invention relates to a method for producing a noble metal article in which a gold coating layer comprising at least two layers of a surface gold coating layer and a base gold alloy layer is formed on at least a part of the surface of a silver clay sintered body made of silver or a silver alloy. A base gold alloy layer forming step of applying a gold coating having a basis weight of 0.2 to 1.2 mg / cm ^{2 on} the surface of the silver clay sintered body and forming the base gold alloy layer by heating and holding; wherein the underlying gold alloy layer is subjected to gold coating having a basis weight 0.4~2.8mg / cm ^2, heating and holding to have a, and a surface gold coating layer forming step of forming the surface metal coating layer, the underlying In the gold alloy layer forming step, heat is maintained at a temperature of 200 ° C. to 420 ° C. for 1 second to 30 minutes, and in the surface gold coating layer forming step, the temperature is 200 ° C. to 350 ° C. for 1 second to 30 minutes. It is characterized by being heated and held .

In the present invention, the surface of the silver clay sintered body is coated with gold, heated to form an alloy on the base gold alloy layer, and then the surface gold coating layer is formed by further heating. Therefore, the base gold alloy layer becomes a gold-silver alloy layer having a silver concentration higher than that of the surface gold coating layer, and in this base gold alloy layer, the surface gold coating layer side has a higher gold concentration than the silver clay sintered body side. Thus, a state in which the composition of gold and silver is inclined can be formed, and the outermost surface (surface gold coating layer side) of the underlying gold alloy layer is a gold-silver alloy having a high gold concentration. The gold-silver alloy is excellent in resistance to sulfidation, and as the amount of gold is increased, generation of black spots due to silver sulfidation can be suppressed. That is, by making the outermost surface of the underlying gold alloy layer a gold-silver alloy having a high gold concentration, the occurrence of black spots due to sulfidation of the silver clay sintered body is suppressed.
In addition, since the base gold alloy layer is a gold-silver alloy in which the composition of gold and silver is inclined and the outermost surface has a high gold concentration, the adhesion of the surface gold coating layer formed on the base gold alloy layer is remarkably improved.
In the present invention, the surface of the silver clay sintered body is coated with gold, and is heated and alloyed to coat the gold on the underlying gold alloy layer, and further heated and baked to form the surface gold coating layer. Therefore, even in a severe use environment such as a ring, a noble metal article having a golden color and a golden color can be obtained over a long period of time.

Gold-coated to form a base metal alloy layer is preferably basis weight 0.2~1.2mg / cm ^2, is less than 0.2 mg / cm ^2, sufficient sulfidation resistance of the noble metal article When it exceeds 1.2 mg / cm ² , the base alloy layer may be peeled off from the silver clay sintered body during the heat treatment. The gold coating to form a surface metal coating layer is preferably 0.4~2.8mg / cm ^2, is less than 0.4 mg / cm ^2, to maintain the golden color of the noble metal article In some cases, the adhesiveness cannot be sufficiently improved when it exceeds 2.8 mg / cm ² .
Further, by setting the heat treatment temperature after gold application for forming the underlying gold alloy layer to 200 ° C. or higher, gold and silver can be sufficiently alloyed by mutual diffusion, and by setting it to 420 ° C. or lower, A desired underlying gold alloy layer can be obtained by appropriately adjusting the progress of alloying. On the other hand, by setting the heat treatment temperature after gold coating to form the surface gold coating layer to 200 ° C. or higher, the base gold alloy layer and the surface gold coating layer can be sufficiently adhered to each other, and 350 ° C. or lower. Thus, the alloying of gold and silver can be moderated and the surface can be prevented from being decolorized to silver.

In the production method of the present invention, in the base gold alloy layer forming step and the surface gold coating layer forming step, a gold colloid liquid obtained by dispersing gold colloidal particles coordinated with a protective agent on the surface of gold particles in a dispersion medium. The gold coating is applied by applying the coating.
The base gold alloy layer and surface coating layer are easily peeled off when formed thick, but the gold colloid solution can be coated in a thin film and the gold concentration can be easily adjusted, making it easy to manufacture precious metal articles. To do.

Silver clay, a sintered body to which the present invention is applied, is widely used as a material for enjoying handmade modeling, such as materials for hobbies and materials for jewelry. Can be applied.
In the method for producing a noble metal article of the present invention, the underlying gold alloy layer can be formed by applying the above-described colloidal gold solution or electroplating with a simple plating tool, and heating the underlying gold alloy layer. The treatment can be performed with a home toaster or the like. Moreover, the surface gold coating layer can be coated with gold by applying the above-mentioned colloidal gold solution or performing electroplating with a simple plating tool a plurality of times. It can be done with a toaster. The home toaster is usually provided with a thermostat so as to stop at about 300 ° C., so that it can be easily heated to a desired temperature range.

  According to the present invention, a noble metal article in which silver sulfidation hardly occurs, a golden shine is maintained over a long period of time even in a severe use environment such as a ring, and a gold coating layer is hardly peeled off. A manufacturing method thereof can be provided.

The layer structure of the surface vicinity of the noble metal article manufactured by the manufacturing method of embodiment of this invention is shown, (a) is sectional drawing, (b) is a graph which shows gold concentration.

Hereinafter, an embodiment of a method for producing a noble metal article according to the present invention will be described.
In the noble metal article 1 to which the manufacturing method of the present embodiment is applied, at least two layers of a base gold alloy layer 3 and a surface gold coating layer 4 are formed on at least a part of the surface of a silver clay sintered body 2 made of silver clay. The gold coating layer 5 provided is formed. This silver clay is produced by adding an organic binder or the like to silver powder made of silver or a silver alloy.

The silver powder is, for example, an Ag fine powder having an average particle diameter of 2 μm or less (preferably an Ag fine powder having an average particle diameter of 0.5 to 1.5 μm): 15 to 50% by mass, and an average particle diameter exceeding 2 μm. Ag powder of 100 μm or less (preferably average particle diameter: 3 to 20 μm Ag powder): obtained by mixing more than 50% to less than 85% by mass.
The organic binder may be any binder such as a cellulose binder, a polyvinyl binder, an acrylic binder, a wax binder, a resin binder, starch, gelatin, and wheat flour. Is most preferred. This organic binder is 0.8 to 8% by mass (preferably 0.8 to 5% by mass) with respect to 50 to 95% by mass (preferably 70 to 95% by mass) of silver powder in silver clay. included.
In addition, fats and oils, surfactants and the like are contained as necessary, and the remainder contains water.
A silver clay sintered body is formed by shaping the silver clay thus produced and heating at a temperature of 550 to 900 ° C. for 5 to 70 minutes, depending on the size of the shaped object.

The noble metal article 1 of the present embodiment includes a base gold alloy layer 3 and a surface gold coating layer 4 provided on the base gold alloy layer 3 on at least a part of the surface of a silver clay sintered body 2 made of silver clay. A gold coating layer 5 having at least two layers is formed. The base gold alloy layer 3 is a gold-silver alloy layer containing gold and silver and having a silver concentration higher than that of the surface gold coating layer 4. In the base gold alloy layer 3, the surface gold coating layer side is more than the silver clay sintered body side. Gold concentration is high. The underlying gold alloy layer 3 is an interdiffusion phase obtained by heating the gold coating formed on the surface of the silver clay sintered body 2 and the silver clay sintered body 2 of the base material. This is an interdiffusion phase obtained by heating the gold coating formed on the gold alloy layer 3 and the underlying gold alloy layer.
The gold coating means for forming the underlying gold alloy layer 3 and the surface gold alloy layer 4 is not particularly limited. Here, gold coating with a gold colloid solution will be described.

The colloidal gold solution is obtained by dispersing colloidal gold particles in an aqueous or non-aqueous dispersion medium or a dispersion medium obtained by mixing these in a predetermined ratio. Colloidal gold particles are composed of gold particles and a protective agent coordinated on the surface of the gold particles.
The protective agent has a carbon skeleton containing nitrogen in the molecule, and has a structure in which the surface of the gold particle is coordinated with nitrogen or an atomic group containing nitrogen as an anchor, and includes an alkoxysilyl group, a silanol group, and a hydroxyalkyl group. The molecular structure includes one or more functional groups selected from the group consisting of groups.

  As an example of a specific method for producing colloidal gold particles, in a non-aqueous system, an alkoxysilane containing a thiol group is obtained by mixing an alkoxysilane containing a thiol group with a gold compound and reducing the gold compound in the presence of a reducing agent. Colloidal gold particles can be obtained in which a protective agent composed of the above alkoxysilane is bonded to the gold particle surface with silane as an anchor. Colloidal gold particles are produced by a nonaqueous reduction reaction in the presence of an alkoxysilane containing a thiol group. Non-aqueous refers to metal reduction of a gold compound in an organic solution such as a thiol group-containing alkoxysilane or alcohol without performing metal reduction in an aqueous solution of the gold compound.

  Colloidal gold particles using a chelating agent such as β-diketone and one or both of the alkoxysilyl group and hydroxyalkyl group chelated with the chelating agent have the effect of delaying the hydrolysis reaction, and are more stable. Increase.

The alkoxysilane preferably contains one or two amino groups and n has an organic chain (—CH ₂ —) n of 1 to 3 inclusive. Specifically, examples of the alkoxysilane having an amino group include γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, and N-β. (Aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane and the like can be mentioned. The amount of these protective agents (amino group-containing alkoxysilane) may be 2 to 40 times in molar ratio to the metal amount.

  As reducing agents, sodium borohydride, trimethylamine borane, dimethylamine borane, tertiary butylamine borane, secondary amine, tertiary amine hypophosphite, glycerin, alcohol, hydrogen peroxide, hydrazine, hydrazine sulfate, formaldehyde aqueous solution Tartrate, glucose, NN-diethylglycine sodium, sodium sulfite, sulfite gas, ferrous sulfate and the like can be used.

  As the gold compound for generating gold particles, chloroauric acid, potassium gold cyanide and the like can be used. The average particle size of the gold particles is in the range of 1 to 100 nm, preferably in the range of 1 to 60 nm. Further, the shape of the colloidal gold particles in which a protective agent is coordinate-modified on the surface of the gold particles is a granular particle having a spherical shape, a polygonal shape or an amoeba shape.

  As described above, the gold colloid particles are dispersed in a predetermined ratio in either a water-based or non-aqueous dispersion medium or a dispersion medium obtained by mixing both of them to prepare a gold colloid liquid. In this gold colloid liquid, the colloid solution is extremely stable because the protective agent for forming the gold colloid particles is firmly bonded to the surface of the gold particles using nitrogen atoms or atomic groups as anchors. be able to. Moreover, even in such a high concentration of gold colloid, the colloid liquid is stable and the viscosity change is small. Furthermore, a thin film having a high film strength can be formed.

As a method for applying the colloidal gold solution thus manufactured, methods such as brush coating, spraying, printing, nozzle discharge, and transfer can be employed.
<Gold alloy layer formation process>
First, the gold colloid liquid is applied to the surface of the silver clay sintered body 2 and then dried and heated to a predetermined temperature to form the underlying gold alloy layer 3. The gold coating for forming the underlying gold alloy layer 3 preferably has a basis weight of 0.2 to 1.2 mg / cm ² . When it is less than 0.2 mg / cm ² , the sulfidation resistance of the noble metal article may not be sufficiently improved. When it exceeds 1.2 mg / cm ² , the adhesion with the surface gold coating layer cannot be sufficiently improved. There is.
The heat treatment temperature after gold application for forming the base gold alloy layer 3 is preferably 200 to 420 ° C. If it is less than 200 ° C., alloying due to interdiffusion between gold and silver may be insufficient, and if it exceeds 420 ° C., alloying proceeds too quickly, so that it may be difficult to obtain a desired base gold alloy layer 3. It is. The heat treatment temperature is more preferably 240 ° C to 320 ° C. The holding time at the maximum temperature may be 1 second to 30 minutes.
After the heat treatment, the underlying gold alloy layer 3 may be polished by buffing or rubbing with a silver polish cloth. At this stage, if the underlying gold alloy layer is polished so as not to be scraped off, the color after the formation of the surface gold coating layer in the next step tends to be improved.

<Surface gold coating layer forming step>
Next, a gold colloid solution is applied onto the underlying gold alloy layer 3 and then dried and heated to a predetermined temperature to form the surface gold coating layer 4. The gold coating for forming the surface gold coating layer 4 preferably has a basis weight of 0.4 to 2.8 mg / cm ² . If it is less than 0.4 mg / cm ² , the golden color of the noble metal article may not be maintained. If it exceeds 2.8 mg / cm ² , the adhesion may not be sufficiently improved.
The heat treatment temperature after gold coating for forming the surface gold coating layer 4 is preferably 200 to 350 ° C. If it is less than 200 ° C., the adhesion between the underlying gold alloy layer and the surface gold coating layer may be insufficient, and if it exceeds 350 ° C., the alloying of gold and silver proceeds and the surface may be decolorized to silver. is there. The heat treatment temperature is more preferably 240 ° C to 300 ° C. The holding time at the maximum temperature may be 1 second to 30 minutes.

In this way, the noble metal article 1 having the gold coating layer 5 having the two-layer structure of the base gold alloy layer 3 and the surface gold coating layer 4 is formed on the surface of the silver clay sintered body 2. In FIG. 1 (a), the boundary of each layer is indicated by a broken line, but in reality, gold and silver are diffused mutually by heat treatment at the interface between the silver clay sintered body 2 and the underlying gold alloy layer 3. The interface between the underlying gold alloy layer 3 and the surface gold coating layer 4 is also diffused and adhered to each other by heat treatment.
Therefore, as shown in FIG. 1 (b), the concentration of gold near the surface of the noble metal article 1 is such that the outermost surface of the surface gold coating layer 4 is the highest, and the concentration gradient is inclined so as to gradually decrease as the depth increases. However, in the vicinity of the interface between the surface gold coating layer 4 and the underlying gold alloy layer 3, a slight discontinuity tends to occur in the concentration gradient.

This noble metal article 1 is a noble metal article whose outermost surface shines in golden color by a surface gold coating layer 4 having a high gold concentration, and the underlying gold alloy layer 3 therebelow has a higher silver concentration than the surface gold coating layer 4. It becomes a gold-silver alloy layer. And this base gold alloy layer 3 is formed in the state in which the composition of gold and silver is inclined so that the gold concentration on the surface gold coating layer side is higher than that on the silver clay sintered body side. The outermost surface (surface gold coating layer side) of the layer 3 is a gold-silver alloy having a high gold concentration. The gold-silver alloy is excellent in resistance to sulfidation, and as the amount of gold is increased, generation of black spots due to silver sulfidation can be suppressed. That is, by making the outermost surface of the base gold alloy layer 4 a gold-silver alloy having a high gold concentration, the occurrence of black spots due to sulfuration of the silver clay sintered body 2 is suppressed.
Further, since the gold alloy layer 3 has a gradient gold and silver composition and the outermost surface is a gold-silver alloy having a high gold concentration, the adhesion of the surface gold coating layer 4 formed on the gold alloy layer 3 is remarkably high. improves.

A colloidal gold solution was prepared by the following procedures (1) to (4).
(1) Stir and mix an aqueous solution of chloroauric acid having a gold concentration of 100 g / l (liter): 40 g, aminopropanol: 30 g, and dimethylamine complex: 0.01 g until the color becomes brown.
(2) The obtained colloidal gold dispersion is precipitated by a centrifugal separator, and the supernatant is discarded. Then, after adding distilled water and shaking, the operation of sedimentation by centrifugation is repeated 3 times for washing.
(3) Taking 0.1 ml of the colloidal gold dispersion after washing and calculating the gold concentration from its dry weight.
(4) Add ethyl alcohol and water so that the gold concentration is 0.1 g / ml and the weight ratio of water: ethyl alcohol is 1: 3 as a dispersion medium.

Next, a commercially available ring-shaped silver clay molded product (PMC Design Ring Flat M2 manufactured by Mitsubishi Materials Corporation) is used as a dedicated alcohol solid fuel using a commercially available dedicated firing pot (silver pot manufactured by Mitsubishi Materials Corporation). Then, the surface of the silver clay sintered body is polished using a number 1500 polishing paper, polished using a luter equipped with a cylindrical felt buff, and then polished with a silver cloth. Thus, eight flat ring-shaped silver clay sintered bodies having a ring size of about 14 whose surface was mirror-polished were prepared.
The firing pot and silver cloth used the contents of a PMC starter kit manufactured by Mitsubishi Materials Corporation.

As shown in Table 1, gold was applied to these silver clay sintered bodies by either electroplating or a method of applying and drying the gold colloid solution, and the conditions shown in Table 1 were also applied. A base gold alloy layer was formed by heat treatment. The electroplating was performed using a commercially available simple plating tool; trade name “Plating Kobo” manufactured by Marui Metal Industry Co., Ltd.
The outer diameter of the ring-shaped silver clay sintered body is defined as the weight increase of the difference between the weight of the silver clay sintered body before gold coating and the weight of the precious metal article after gold coating and heat treatment. The surface area of the silver clay sintered body was calculated from the inner diameter dimension and the width dimension, and the value obtained by dividing the gold coating weight by the surface area was calculated as the gold coating weight, and the values are shown in Table 1.
As a comparative example, a silver clay sintered body that does not form a base gold alloy layer was used.

  Next, the obtained ring-shaped silver clay sintered body was cut into two in a semicircular shape, and the gold concentration on the surface and the gold in the depth direction were analyzed by Auger spectroscopic analysis for the base gold alloy layer of one sample. Distribution was measured. The gold concentration on the surface was measured at 10 points, and the average value is shown in Table 1. The gold distribution in the depth direction is measured by measuring the gold concentration while etching the sample surface with argon, and the argon etching at that time is performed when quartz having a purity of 99.9% or more is used as a standard sample. The thinning rate was 5 nm / min. From the measurement result of the obtained gold distribution in the depth direction, an argon etching time in which the gold concentration is 20% of the gold concentration on the surface is obtained, and a value obtained by multiplying the argon etching time by the thinning rate of the quartz is converted into quartz. The thickness was calculated as shown in Table 1.

Next, with respect to the remaining semicircular sample that was not used for analysis among the cut silver clay sintered body, gold was applied and heat-treated according to the method and conditions shown in Table 2 to form a surface gold coating layer. Formed. The obtained surface gold coating layer was visually observed to confirm the presence or absence of peeling, and the results are shown in Table 3.
Next, as a sulfidation resistance test, an aqueous solution of an anti-smudge solution prepared by dropping 5 drops of an squirt solution (manufactured by Nippon Ceramic Science Co., Ltd., in an eye drop type container) into 200 ml of pure water was prepared. The sample was immersed in an aqueous solution for 30 seconds, and the presence or absence of black spots was visually observed. Table 3 shows the results.

As is apparent from the results in Table 3, Comparative Examples 1 to 4 in which the base gold alloy layer was not formed peeled off, became a silver color by heat treatment, or were immersed in a squirt solution due to sulfidation. Black spots have occurred. On the other hand, the examples have no peeling and are golden in color, and black stains are not generated even when immersed in the smoldering liquid.
Furthermore, when one of Example 1 was prepared separately and both were worn on the right-handed ring finger and spent two months of daily life, the size of about 0.5 mmφ was rubbed against the steering wheel when driving a car. Although the golden color was peeled off and the underlying silver color appeared, the other parts remained golden.

DESCRIPTION OF SYMBOLS 1 Precious metal article 2 Silver clay sintered body 3 Underlying gold alloy layer 4 Surface gold coating layer 5 Gold coating layer

Claims (1)

A method for producing a noble metal article in which a gold coating layer comprising at least two layers of a surface gold coating layer and a base gold alloy layer is formed on at least a part of the surface of a silver clay sintered body comprising silver or a silver alloy,
A base gold alloy layer forming step of applying a gold coating having a basis weight of 0.2 to 1.2 mg / cm ^{2 on} the surface of the silver clay sintered body and heating and holding to form the base gold alloy layer;
Wherein the underlying gold alloy layer is subjected to gold coating having a basis weight 0.4~2.8mg / cm ^2, heating and holding to have a, and a surface gold coating layer forming step of forming the surface metal coating layer,
In the base gold alloy layer forming step, the temperature is maintained at a temperature of 200 ° C. to 420 ° C. for 1 second to 30 minutes,
The method for producing a noble metal article, wherein in the surface gold coating layer forming step, heating and holding are performed at a temperature of 200C to 350C for 1 second to 30 minutes .

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