HK1072750B - Method for manufacturing an ornamental article and gemstone suitable for such method - Google Patents

Description

Method for manufacturing ornament and ornament jewel suitable for the method

Technical Field

The present invention relates to a method for manufacturing a ornament by casting a metal around an ornament gemstone, and to an ornament gemstone to which the method is applied.

Background

This method is particularly suitable for relatively precious stones, where the manufacture of a part of the piece of jewellery separately from a precious metal and its bonding with the stone by a gold artist represents a relatively expensive expense.

In particular, the gemstones used in this type of method are those which artificially accentuate or change their natural color. There are two principally different methods available for the change of the colour of the gemstone: it is possible to let the colored element penetrate into the gemstone or to firmly bond a colored, for example pigmented, layer to the gemstone.

Only the second method of changing color is of interest here because it is more suitable for industrial mass production. It is known, for example, from US 3,837,884(Balzers) to apply a blue layer to a substrate by spraying cobalt oxide, aluminum oxide and silicon oxide. Although this coating is tempered in an oxygen-containing atmosphere at about 300 ℃ for about 30 minutes, it is not stable under the conditions of this process.

Disclosure of Invention

Starting from this, it is an object of the present invention to provide a method for producing a piece of jewellery, in which the problem of an unstable colour coating of the gemstone in the production of a piece of jewellery by casting the gemstone around with metal is overcome.

To this end, the invention provides a method for manufacturing a piece of jewellery by casting around a metal a jewel of the item, characterized in that: the jewelry jewel is provided with a color-changeable pigment-containing coating prior to being cast around and the coating is subjected to an energy treatment during or after the application of the coating which causes the coating to undergo a transformation which would occur if the jewelry jewel was cast around without the energy treatment, whereby the color of the coating is no longer significantly changed by the energy treatment when heated to a temperature below 1250 ℃.

It has been unexpectedly found that jewelry gemstones provided with a colored coating can be treated in a casting process if it is set that the coating is subjected to an energy treatment during or after its application which causes the coating to undergo a transformation which would otherwise occur when the jewelry gemstones are cast around without the energy treatment.

In the case of the fixture machining specified at the outset, the gemstone is initially held for a relatively long time at a temperature at which the wax model burns, which should eventually be replaced by the poured precious metal. This temperature is approximately 750 ℃. The surface of the stone is then heated to a temperature, during the precious metal pouring, of between 950 ℃ and 1050 ℃ for silver, 950 ℃ to 1250 ℃ for gold and 1800 ℃ to 1900 ℃ for platinum. As will be discussed below with reference to the examples, the stones of the coloured layer are heated only for a short time to the casting temperature of the metal and/or for a longer time to the burning temperature of the wax pattern in order to minimize the colour change that occurs during casting itself.

Accordingly, the present invention also provides an ornamental gemstone suitable for making an ornamental article according to the above method, wherein the ornamental gemstone is provided with a variable colour pigmented coating, the colour no longer being significantly altered by energy treatment when heated to a temperature below 1250 ℃.

Drawings

The details of the invention are explained in more detail below with the aid of the figures and examples.

Fig. 1-3 are schematic diagrams of three common stages of the process of the present invention.

Fig. 4 is a partial cross-sectional view of a trim piece made in accordance with the present invention.

Detailed Description

It is known to manufacture a piece of jewellery by casting a gemstone around metal, as shown in fig. 1, the gemstone 1 being placed in a mould material 5, while for the base metal first wax 6 is used as a position holder. The wax 6 is then tapped by heating it to about 750 c to form the cavity 7 shown in figure 2. Finally, the cavity 7 is filled with metal 4 according to fig. 3, which surrounds the gemstone 1.

In figures 1-3 a ring is shown as an example of a piece of jewellery, but the invention can be used broadly where the surface of the gemstone, particularly the back surface 2 (see figure 4) is provided with a coloured coating that may be damaged by pouring in metal 4.

The method of the invention is based on the premise that the optical properties of the gemstone itself remain unchanged during the casting around with metal. Glass and crystal can be provided with a heat-resistant color layer without difficulty, for example, but ordinary glass melts at a predetermined temperature. The crystal is already opaque at the normal temperatures at which the wax burns.

Basically suitable gemstones, such as zirconia, are now provided with a layer of colour. The most common methods for this are vapor coating, spraying, chemical vapor coating, and the like. In particular, it is possible to apply most inorganic pigments directly to slightly heated substrates by reactive sputtering, even at low temperatures.

For the coloration of gemstones, it is known to use as inorganic color pigments, in particular with regard to their basic chemical composition, in particular inorganic materials having a "texture" (Strich). Such pigments are known in connection with surface pigments for ceramic glazes and also for glass. In particular, pigment layers based on oxidic pigments having a rutile-cassiterite-, zircon-, baddeleyite, corundum-hematite-, olivine-, spinel-, garnet-and perovskite structure are to be preferred. Nitride and especially oxynitride pigment-based pigment layers as well as carbide and carboxylate-based pigment layers are also very suitable for the present method. Pigment layers based on sulfides, sulfates, phosphates, cyanides and metal colloids require special inlaying, but it is even more suitable if they have a melting point close to or slightly below the casting temperature.

If the working of a gemstone thus prepared in advance according to the method of fig. 1-3 is continued, an unintended and completely uncontrolled staining of the gemstone may result. This staining was rated according to the "stained gemstone grading System" of the American Geology Institute (Gemologic Institute of America). Here, hue, "luminosity" (light/dark) and color saturation are assessed. The effect achieved by the invention is that the gemstone, which has been coloured and has been cast without any particular subsequent treatment to produce a change in the at least two points according to at least one of the criteria listed, now exhibits a maximum of two, usually a maximum of one, deviations. This is achieved by an energy treatment which predicts the loads occurring during wax burning and metal casting.

Some examples of carrying out the method of the invention are provided below. The marking of the pigment used here is carried out by means of the CAS-registry number data of the American chemical society. Pigments suitable for high temperatures are available in Ullmann's Encyclopedia of Industrial Chemistry 1986, volume A5, especially page 546/547. These pigments can be produced according to the invention directly or by selecting a suitable intermediate layer, inlay or cover layer in such a way that they do not change their color during casting.

Example 1 (comparative experiment):

a coating of about 35% by weight of cobalt oxide, 10% of aluminum oxide and the balance silicon oxide was deposited on cubic zirconium oxide (Zirkonia) by the method described in US 3,837,884. A blue coating is produced by subsequent heat treatment. The casting of gemstones with a dye layer facilitates the staining of the gemstones without subsequent treatment at the casting temperature of 14ct gold (about 1050 c).

According to the novel process of the invention, the coated gemstone is heated to 1200 ℃ for 10 minutes and then annealed at 750 ℃ (which corresponds to the wax burning temperature) for one hour. Even at the 14ct palladium-platinum casting temperature (1250 ℃), no subsequent color change is caused by the heat treatment.

Example 2 (comparative experiment):

coating of CAS68186-85-6 composition (Green spinel, Co) by reactive sputtering (Reaktiv-Sputten) on zirconia at low temperatures₂TiO₄) With a slight excess of TiO₂The pigment of (1). A noticeable change in green color was caused at the casting temperature of 14ct palladium-platinum.

Whereas if the coating is annealed at 1200 c for one minute, the coated gemstone will not exhibit a discernible change in color at the casting temperature.

However, if the gemstone, annealed at 1200 deg.C, is cast with a 14ct gold melt, a brownish color change results. The color change is most intense at the edge portion of the color layer in direct contact with the alloy.

If the colour layer is coated with a protective layer consisting of magnesium aluminate and the stone is annealed at 1200 c, the colour tone does not change even in the area in direct contact with the high temperature gold alloy.

Example 3:

by applying a thin SiO layer₂The process of applying iron oxide pigments in layers together with a mosaic matrix of aluminum oxide, makes it possible to produce a pigment with CAS68187-35-9 (brown hematite, Fe) in a temperature-stable and chemically and mechanically stable manner₂O₃) A base color layer. After a treatment time of 10 minutes at 1200 ℃ and a subsequent treatment time of 2 hours at 750 ℃, the colour tone of the mosaic and heat-treated pigment no longer corresponds completely to that of the pure pigment, but the colour does not change during casting.

Example 4:

CAS 68187-05-3 pigment for zirconia with basic chemical formula of Co₂SnO₄Of the lime brown spinel, is coated. A pigment layer of approximately 125mm is covered with a dense protective layer consisting of aluminum oxide and heated to 1200 ℃ for one minute, followed byThe stone was annealed in air at 750 c for 30 minutes. The blue color thus formed remained unchanged at the coinage silver (Sterling Silber) casting temperature.

It is contemplated in each of the examples listed that the colored layer of the jewelry jewel may not be damaged only by the temperatures that occur during the metal casting. Furthermore, undesired variations may be caused at the interface between the gemstone and the color layer, especially at the outer surface of the color layer, which may be avoided by the separation layer. In particular, this takes into account the fact that, even for natural-color gemstones, the gloss may be impaired during the metal casting.

If the painted back of the stone is also intended to prevent mechanical effects, in particular the impact of protective abrasive particles or other pieces, and the abrasive action of the diamond abrasive, it is possible to envisage surrounding the back of the stone with a ring made of cast metal, as shown in fig. 4.

Claims (8)

1. A method of making a piece of jewelry by casting metal around a jewelry gemstone, characterized by: the jewelry jewel is provided with a color-changeable pigment-containing coating prior to being cast around and the coating is subjected to an energy treatment during or after the application of the coating which causes the coating to undergo a transformation which would occur if the jewelry jewel was cast around without the energy treatment, whereby the color of the coating is no longer significantly changed by the energy treatment when heated to a temperature below 1250 ℃.

2. The method of claim 1, wherein: the energy treatment comprises heating to a temperature between 950 ℃ and 1250 ℃ in a time of 1 to 20 minutes.

3. A method as claimed in claim 1 or 2, characterized by: the energy treatment comprises annealing at a temperature between 700 ℃ and 800 ℃ for a period of at least one hour.

4. The method of claim 1, wherein: the pigmented coating is provided with a protective cover layer.

5. The method of claim 4, wherein: the capping layer contains lithium, magnesium, zinc, boron, cerium, titanium, silicon, zirconium, or aluminum.

6. The method of claim 1, wherein: a transition layer is arranged between the ornament jewel and the color coating.

7. The method of claim 1, wherein: the back (2) of the jewellery stone (1) is protected by a ring (3) made of cast metal (4).

8. Ornamental gemstone suitable for manufacturing an ornament by casting around with metal according to the method of any of claims 1 to 7, characterized in that: the jewelry gemstones are provided with a variable color pigmented coating, the color no longer changing significantly upon heating to a temperature below 1250 ℃ as a result of energy treatment.