There are few metals that exist in Nature in a pure and isolated state. Most are found combined with other substances (oxygen or acids). Gold, copper, and silver are the exception.
The primary raw materials used in the production of filigree pieces are gold and silver, precious metals that are compatible with the elaborate, difficult, meticulous, and complex technique of filigree. They can coexist, in the same piece, with other materials and techniques, such as enamels, stones, various metals, leather, cork, textiles, etc. But in this case, these are not pieces in the “100% filigree” category. They may be in the “filigree” category (where more than 50% of the piece must consist of filigree work) or “filigree applications” (see chapter 6 – Characteristics of the product “Filigrana de Portugal”).

Filigree is not considered to be work in wires of non-precious metals (copper, wire, etc.), regardless of possible twisting of the wires and the filling of the pieces: the complexity of the technique demands that only gold and silver, noble metals that, due to their characteristics, do not compromise the final results and confer to filigree its value (real and symbolic), rarity, brilliance, beauty, and uniqueness, are admitted.

• Gold
Gold, considered the noble metal par excellence, is practically indestructible under the action of chemical agents, as well as in contact with the environment, whatever the temperature. It does not change under the action of heat or humidity, nor with the corrosive agents in the air. The fact that it is a stainless metal par excellence, brilliant (golden color) and incorruptible, associated with its relative scarcity, has made it the most appreciated and sought-after metal for ornamental purposes.

Gold is an extremely dense metal. But it is also the most malleable metal (it can undergo permanent deformations when subjected to certain temperatures and some mechanical actions) and the most ductile (it can be reduced to very fine wires). Too fragile and flexible to be used pure in jewelry pieces, it needs to be mixed with other metals, which gives it greater strength. In filigree objects (as well as in all art and luxury objects), an alloy with copper and silver is used.

In Portugal, the percentage of gold in the composition of the alloy per kilogram is 800 grams of pure gold (80%) and 200 grams for the remaining components of the alloy (20%). It is known as 19.2-carat gold. There are also cases where the percentage of gold is 75% to 25% alloy (known as 18-carat gold).
In colored gold pieces, depending on the desired hue, the alloy contains gold, silver, and copper, with the variation in the proportion of these two metals giving a more reddish tone (higher copper content) or more yellow (higher silver content).

The gold wire in filigree work must be thin (becoming much more malleable and “plastic” and allowing for extremely meticulous and detailed filigree work), and its maximum thickness should not exceed 0.22mm.

• Silver
After the discovery and use of gold and copper, other metals such as tin, silver, and lead appeared. The similarity of the characteristics of silver to those of gold led to it also being used in the manufacture of ornaments and for decorative purposes.
Silver is a white-colored metal that, like gold, is practically unalterable in air and water. It is very ductile, malleable, and resistant to corrosion, and it is the substance with the highest thermal and electrical conductivity. Despite its metallic shine, silver oxidizes in contact with air, losing its characteristic color and shine.
In silver filigree objects, the alloy for the filling wire is composed of silver and copper, in the proportion of 95% silver and 5% copper, and a silver alloy in the proportion of 92.5% silver and 7.5% copper can be used in the making and execution of the skeleton or framework.
The silver wire in filigree work must have a maximum thickness of 0.22mm.

• Hallmarking
To certify the quality of the alloys used (“assay”), there is a control system consisting of the affixing, on the pieces, of a mark (stamp) by the Casa da Moeda (the entity with national authority to supervise and guarantee the metal content in alloys – assay).
The control and marking of precious metal artifacts is the oldest form of consumer protection. The falsification of jewelry artifacts was, in the past, a crime severely punishable by law, similar to the falsification of currency. D. João I (1357-1433) regulated the profession of goldsmith and the jewelry trade. Subsequently, the Afonsine Ordinances (1446) and the Philippine Ordinances (1603) increased the penalties, which ranged from exile to the death penalty. With D. Pedro II, in the 17th century, the minimum assay for gold became 20 carats, and during the reign of D. João V, in the 18th century, it became 18 carats, and the quality of the alloys was mandatorily examined by overseers. Currently, the Penal Code provides for severe penalties for the falsification of hallmarking stamps. During the Middle Ages, the control of the assay of precious metals (percentage of precious metal in the alloy) was the responsibility of the goldsmiths' guilds. There was the Confraternity of Goldsmiths of Lisbon, the Confraternity of Silversmiths of Lisbon, and their counterparts in Porto, which followed very strict regulations to ensure the quality levels of the manufactured articles. It was the responsibility of the Casa da Moeda, acting “in the name of the King,” to supervise the activity. With the disappearance of the guilds in 1834, the task and responsibility of “hallmarking” precious metal artifacts was given to the municipalities, a system that proved to be ineffective. As a result, the marks and Portuguese jewelry lost some of their credibility. In 1881, King D. Luís I decreed the standardization of gold and silver assays throughout the country. A year later, and to consolidate previous control and inspection measures, Fontes Pereira de Melo abolished the municipal assays and decreed the creation of the Lisbon and Porto Assay Offices, under the Casa da Moeda. In 1886, the Braga Assay Office was created, which was later extinct in 1911. In 1900, the creation of a new assay office in Gondomar was requested from the Government, given the number of manufacturers existing there, and this office was created in 1913. With the creation of Imprensa Nacional-Casa da Moeda in 1972, the Assay Offices were integrated into this public company. In 1986, the current Department of Assay Offices of the Imprensa Nacional-Casa da Moeda was created, integrating the Lisbon and Porto Assay Offices, the latter including a branch in Gondomar, a situation that still exists today. Under the Legal Regime of Jewelry and Assay Offices, approved by Law no. 98/2015, of August 18, articles with precious metal, such as gold and silver, must obligatorily be hallmarked to guarantee the consumer the quality and authenticity of the metals/alloys used, a requirement naturally mandatory for access to the certification of the pieces as “Filigrana de Portugal.” There must also be a punch with the certification mark, affixed to the piece by the goldsmith (in a place chosen by him and with the size that each workshop deems best for each piece where it will be applied), identifying the piece as Filigrana de Portugal, a certified traditional artisanal technique.

_{Source: Ramos, Graça, Specification Book for Certification, 2017}