WO2012017299A1

WO2012017299A1 - Alloy for goldware, jewellery and similar products, and products produced from this alloy

Info

Publication number: WO2012017299A1
Application number: PCT/IB2011/001809
Authority: WO
Inventors: Pasquale Bruni Bossio
Original assignee: Pasquale Bruni S.P.A.
Priority date: 2010-08-04
Filing date: 2011-08-03
Publication date: 2012-02-09
Also published as: ITAL20100004A1; IT1401401B1; EP2601325A1

Abstract

Alloy for goldware, jewellery or the like products consisting of: gold in a total amount from 4 to 4.5 weight %; silver in a total amount from 35 to 68 weight %; palladium in a total amount from 8 to 30 weight %; one or more elements selected from iridium, copper, zinc, nickel, and silicon in a total amount from 18 to 32 weight % or indium in a total amount from 25 to 32 weight%, and optionally one or more further components in a total amount up to 3 weight %.

Description

ALLOY FOR GOLDWARE, JEWELLERY AND SIMILAR PRODUCTS, AND PRODUCTS PRODUCED FROM THIS ALLOY

The present invention relates to an alloy for goldware, jewellery and similar products, and more specifically to a gold alloy for goldware, jewellery and similar products.

Prior art

It is common knowledge that gold is a precious metal typically used in jewellery and goldsmithing for the production of necklaces, rings, charms, bracelets, and the like. With regard to the technical aspects of the manufacture of ornaments, pure gold, known as 24 carat gold, is easy to work but has the disadvantage of being susceptible to damage because it is relatively "soft", that is to say highly malleable, and therefore has little resistance to shear forces. Consequently, gold alloys with purities varying between 9, 14 and 18 carats are normally used.

It should be noted that, where gold alloys are concerned, the term "carat" has a different meaning from that of the unit of weight used for gems and pearls, being used as a measure of "purity" to quantify the proportion of gold on a 24/24 basis. In the case of gold alloys, therefore, a carat is equivalent to one part of gold in 24 parts of metal constituting the alloy. It follows that "18 carat", for example, signifies that an alloy contains 18 parts of fine gold and 6 parts of other alloying metals. The term "carat" is abbreviated to "ct" or "kt", or commonly to the single letter "k", often following the number with no intervening space, for example 18k. Gold of maximum purity is therefore described as 24 carat (24 parts of "fine" gold out of a total of 24) and is denoted by the symbol 24k. The remainder of the alloy is typically composed of alloying metals, usually comprising silver and copper.

In the industry, and where gold ornaments are concerned, the minimum content of gold in an alloy is 9 carat, which is considered to be the minimum level required in an ornamental article in order to impart satisfactory colour tone and brilliance of the gold.

As is known, gold alloys in the range from 9 to 10 carats have hitherto been less attractive in terms of colour tonality. These alloys, containing the aforesaid ratio of gold to copper by weight, have a rather reddish colour, although they are markedly easier to work (since they are tougher). There is also the disadvantage that these alloys are more sensitive to oxidation and therefore become increasingly reddish over time.

As a general rule, goldware made from these alloys is subsequently plated with gold alloys of 16 carats or above, or even with pure gold, to compensate for the lack of colour tonality and oxidation resistance. JP2000192170 describes a low-carat corrosion-resistant gold alloy of enhanced golden color with non-blackening casting skin, the principal components whereof are gold 2-30%, palladium 15-35%, indium 5-22%, copper 0.5 -12%, zinc 0.1 - 10% and a balance of silver. This low-carat gold alloy is particularly used as a cast gold alloy for dental crowns and for general decorative application. JP2000192170 discloses specifically a previously known alloy consisting of 5% Gold, 30% Palladium, 40% Silver and 25% Copper, but noted that the casting skin colour at casting and resistance to discoloration and corrosion were inferior. It taught to overcome these problems by alloying with indium and increasing the gold content to a percentage ranging from 12 to 16. An alternative way to deal with these problems would be to plate with high-carat gold.

The object of the present invention is therefore to provide an alloy with a low gold content which resolves the aforesaid problems, and which has a colour tonality comparable to that of a high-purity gold alloy while also having good physical and chemical characteristics.

Another object of the present invention is to provide an alloy with a low gold content which is not subject to changes of colour over time, and which does not vary in brilliance over time.

A further object of the present invention is to provide an alloy with a low gold content which has good workability combined with a low production cost, and which is therefore of considerable commercial value.

Yet another object of the present invention is to permit the manufacture of articles of jewellery which are larger and more portable because of the lower weight of the metal.

An even further object of the present invention is to provide an alloy which has attractive colour change to the light exposure. In summary, the prior art discloses a galvanic treatment in order to make the object resistant against the blackening effect. The inventive one carat gold alloy, on the contrary, does not require any treatment on the surface of the metal, due to the fact the primary objective of the invention is to create an alloy which allows the surface of the object to change colour according to the light exposure. With daylight it will assume a light pink tone, almost white, while with low light it will become an intense pink. The main principle of the invention is that the combination based on one carat gold and various other alloying elements with no additional surface treatment such as plating, can create a different range of colours based on the light irradiation of the moment, either natural or artificial light. Brief description of the invention

Accordingly, the present invention provides an alloy for goldware, jewellery or the like product consisting of:

- Gold in a total amount from 4 to 4.5 weight %

- Silver in a total amount from 35 to 68 weight %

- Palladium in a total amount from 8 to 30 weight %

- One or more elements selected from iridium, copper, zinc, nickel, and silicon in a total amount from 18 to 32 weight % or indium in a total amount from 25 to 32 weight%, and

- Optionally one or more further components in a total amount up to 3 weight %, in particular a catalyst such as borax in a total amount from 0.02 to 0.05 weight %, and/or, in a preferred embodiment, platinium in a total amount from 0.05% to 1% or from 0.1 to 1 weight %.

In one embodiment of the inventive alloy, silver is in total amount from 60 to 68 weight %, and palladium is in total amount from 8 to 15 weight %.

In another embodiment of the inventive alloy, silver is in total amount from 30 to 38 weight %, preferably 35-36 weight %, palladium is in total amount from 28 to 35 weight %, preferably 29-30 weight %, and indium is in total amount from 25 to 32 weight %, preferably 29-31 weight %.

In another embodiment, silver is in a total amount from 50 to 55 weight % and palladium is in a total amount from 15 to 20 weight %.

In yet another embodiment, silver is in a total amount from 40 to 50 weight %, palladium is in a total amount from 20 to 30 weight % and possibly from 25 to 30 weight %, In this and the other embodiments, the element(s) selected from iridium, copper, zinc, nickel, and silicon can be in a total amount from 20 to 25 weight %, the most usual preferred alloying element from this group being copper. In all these embodiments of the inventive alloy, gold is advantageously in a total amount from 4.16 to 4.18 weight %, typically 4.16 weight %.

Detailed description of the invention

A detailed description of a preferred embodiment of the gold alloy of the present invention will now be given with reference to exemplary embodiments provided by way of non-limiting example. Exemplary embodiments

Preliminary experiment

In order to produce a gold alloy for articles of jewellery which contains 4.16% gold (equivalent to one carat gold) but which has a colour, brilliance and workability typical of commercial gold alloys, the present inventor has carried out a first experimental melt in his laboratories, using an induction furnace and graphite crucible, with a mixture of the following elements:

- pure silver: 19.14 grams

- pure gold: 0.86 grams.

A gold cylinder was produced, with a net weight of 20 grams, rated at 1 ct gold (in practice, the eighteenth part of the gold normally contained in an alloy with a millesimal fineness of 750, known as an 18 ct alloy).

The cylinder produced in this way showed evident defects in the form of incomplete mixing of the two metals. Although the silver and gold had melted together, they had remained almost completely separate, as demonstrated by the coloration of the cylinder which had clearly distinct yellow and white areas.

Example 1

A second experimental melt was carried out, using an induction furnace and graphite crucible, with a mixture of the following elements: - gold: from 4.16% to 4.18% by weight with respect to the total weight of the mixture;

- silver: from 40% to 50% by weight with respect to the total weight of the mixture;

- platinum: from 0.1 % to 1 % by weight with respect to the total weight of the mixture;

- palladium: from 25% to 30% by weight with respect to the total weight of the mixture, and

- One or more elements selected from iridium, copper, zinc, nickel, and silicon in a total amount from 20 to 25 weight %.

The result was a cylinder of 1 ct gold with a net weight of approximately 25 grams. The resulting cylinder shows a considerable uniformity of mixing of the two principal metals (gold and silver). The silver and gold had completely melted into each other. The coloration of the cylinder was uniform and did not show any markedly distinct areas of colour.

Example 2 A third experimental melt was carried out, using an induction furnace and graphite crucible, with a mixture of the following elements:

- gold: from 4.16% to 4.18% by weight with respect to the total weight of the mixture;

- silver: from 50% to 55% by weight with respect to the total weight of the mixture;

- Palladium: from 15 to 20% by weight with respect to the total weight of the mixture;

- Platinum: 1 % by weight with respect to the total weight of the mixture, and

- Copper: 20 to 25% by weight with respect to the total weight of the mixture. Example 3

A fourth experimental melt was carried out, using an induction furnace and graphite crucible, with a mixture of the following elements:

- gold: 4.16% by weight with respect to the total weight of the mixture;

- silver: 65% by weight with respect to the total weight of the mixture;

- Palladium: 9% by weight with respect to the total weight of the mixture;

- Platinum: 1 % by weight with respect to the total weight of the mixture, and - Copper: 20,84% by weight with respect to the total weight of the mixture.

Example 4

A fifth experimental melt was carried out, using an induction furnace and graphite crucible, with a mixture of the following elements:

- Gold: 4.16% by weight with respect to the total weight of the mixture,

- Silver: 35.80% by weight with respect to the total weight of the mixture,

- Palladium: 29.85% by weight with respect to the total weight of the

mixture,

- Indium: 30% by weight with respect to the total weight of the mixture,

- Various binding elements: 0.19% by weight with respect to the total weight of the mixture.

This provided a yellow gold alloy. Tests of workability were conducted on the alloy of examples 1 to 4, and the resulting alloys show practically the same physical and mechanical characteristics as the gold alloy with a low content, known commercially as 14 ct gold alloy. The alloy of the present invention has the following principal advantages:

There is a commercial advantage, in the form of the costs of the product, given the present cost of gold. From 18 carats to 1 carat, the cost decreases considerably, and consequently there is a financial benefit (current gold prices range from€28 to€30 per gram) in producing lighter articles, since gold is a very heavy metal. Therefore this represents a saving in cost.

Another advantage is the greater portability of articles to be worn, especially in the case of large objects, due to the lower weight of the metal. Indeed, the specific weight of 24 carat gold is 19.25 g/cm³, whereas the specific weight of 1 carat gold is approximately 10 g/cm³.

Another advantage is that the resulting articles, while having a lower percentage of gold, have the same optical characteristics as the original 18 carat gold from which they were produced. The invention can be used for both yellow gold and white gold, and also for all types of coloured gold (yellow, white, red, green, black, etc.). It is clear from the above description that the invention is not limited to the embodiments which are described herein purely by way of non-limiting examples, but can be considerably varied and modified in its entirety and in respect of its details, especially as regards construction and the use of technical and functional equivalents, in order to meet specific requirements of manufacturing and use and to facilitate these processes, without departure from the guiding principle described above and claimed below.

Claims

Alloy for goldware, jewellery or the like product consisting of:

- Gold in a total amount from 4 to 4.5 weight %

- Silver in a total amount from 35 to 68 weight %

- Palladium in a total amount from 8 to 30 weight %

- One or more elements selected from iridium, copper, zinc, nickel, and silicon in a total amount from 18 to 32 weight % or indium in a total amount from 25 weight % to 32 weight%, and

- Optionally one or more further components in a total amount up to 3 weight %.

Alloy according to claim 1 , wherein silver is in total amount from 60 to 68 weight %, and wherein palladium is in total amount from 8 to 15 weight %.

Alloy according to claim 1 , wherein silver is in a total amount from 50 to 55 weight % and wherein palladium is in a total amount from 15 to 20 weight %.

Alloy according to claim 1 , wherein silver is in a total amount from 40 to 50 weight %, wherein palladium is in a total amount from 20 to 30 weight % and possibly from 25 to 30 weight % and wherein one or more elements selected from iridium, copper, zinc, nickel, and silicon is in a total amount from 20 to 25 weight %.

Alloy according to claim 1 , wherein silver is in a total amount from 30 to 38 weight%, preferably 35 to 36 weight%, wherein palladium is in a total amount from 28 to 35 weight%, preferably 29-30 weight%, and wherein indium is in a total amount from 25 to 32 weight %, preferably 29 to 31 weight%

6. Alloy according to any of the preceding claims, wherein said further components are a catalyst such as borax in a total amount from 0.02 to 0.05 by weight %.

7. Alloy according to any of the preceding claims, wherein said further components comprise platinum in a total amount from 0.05 to 1 weight %.

8. Alloy according to claim 7, comprising platinum in a total amount from 0.1 to 1 weight %.

9. Alloy according to any of the preceding claims, wherein gold is in a total amount from 4.16 to 4.18 weight %.

10. Alloy according to claim 8, wherein gold is in a total amount of 4.16 weight %.

11. Use of the alloy according to any of the preceding claims in the production of a article of jewellery or a timepiece.

12. An article of jewellery or a timepiece comprising the alloy according to any of claims 1 to 10.