Portoro Marble: the Italian black and gold natural stone

Portoro Marble, also known as black and gold marble, is a fine variety of Italian marble from the charming Golf of Poets, in the Ligurian province of La Spezia. It is one of the most beautiful among the polychromatic marbles. This precious Italian stone consists an intense and bright black colour with gold veins running through it that range from intense yellow to honey colour.

The peculiarity of its appearance makes it a unique marble, irreplaceable as an ornamental stone. There is no stone similar, in luxurious sophistication or characteristic, to this black and gold beauty. Portoro is a natural work of art, in front of which it is easy to become enchanted.

Characteristics of black Portoro marble

The geological composition of Portoro is calcareous with a microcrystalline structure. Marine substances are responsible for the dark colour and also the golden veins, which are a product of the organic marine materials oxidising. The microcrystalline structure contributes to the particularity of the Portoro and also renders the stone more compact.

The deep and intense black colour of this marble gives the appearance of an almost velvety texture, which is particularly observable when the slabs are polished. These polished slabs look as if gold has been poured directly onto the stone. The veins, streaks, spots and shadows of this black and gold marble are the result of  pyrite and ocher-limonite substances.

The uses of Portoro marble

Portoro is commercially considered suitable for many different uses: for artistic application, columns, church and palace interiors, cladding, flooring and furniture tops. The polished finish is preferred as it adds a level of elegance. This black and gold marble, given its unique veins and high cost, is often used in luxury residences, prestigious hotels and affluent villas. Portoro is frequently used as an inlay, as it creates a perfect contrast when combined with a light coloured marble.

Typologies of Portoro black and gold marble

Based on the intensity of the colours, both the dark background and the veins, Portoro marble has several variations in quality. Starting from the top and working our way down, we can distinguish five different types or levels of quality:

• The first consists of a black background with thin gold veins. This typology is called ‘fine spot’.
• The second has the usual black background and gold veins however these veins are slightly wider than the previous ones and are arranged in the shape of a catenary.
• With the third the black background and yellow veins remain however they are more faded and tending on white and flanked by white patches.
• The fourth is characterised by very faded veins and wide white spots.
• The last has the classic background but with white veins and white spots.

The most precious variety are the typology in which the yellow veins are more present. The other varieties, with veins and spots that are nearly white, are also widely requested due to, despite being less valuable, their superior resistance.

Portoro marble quarries

Theoutcrops ofPortoro, which are used for extraction, are present exclusively in the La Spezia province, extending from the Tinetto, Palmaria and Tino islands towards Portovenere. The landscape and environment of these beautiful places are delicate, therefore the cultivation of the quarries is carried out with particular attention.

The current number of quarries is very limited in comparison to the last century, the blocks are extracted from large chambers whose vaults are supported by pillars to avoid any impact on the landscape. On the Istituto Luce website there is a short video showing the mining of Portoro quarries back in 1932.

Other outcrops of Portoro are also resent in Tuscany, in the Apuan Alps and Umbria, although they do not present the characteristic features of the Portoro extracted in Liguria.

The history of Portoro marble

We do not know the exact starting date of the exploitation of the Portoro marble deposits, we presume that the quarrying for this black and gold marble was already taking place during Roman times. Initially, small blocks of stone were detached to be used, mainly, in the construction of houses, then gradually Portoro was exploited for more purposes. Buildings adorned in Portoro became more prominent.

The first uses of Portoro marble date back to the Roman Imperial villas, and probably to the temple of Venus which overlooks the Gulf of La Spezia, above which the church of San Pietro was built. Even in the ancient Roman colony of Luni, which extended into territories of La Spezia which still exist today, there is evidence of Portoro having been used in the perimeter walls of the amphitheatre.

During the reign of Cosimo I de’ Medici there was a great push for the research and extraction of polychrome marbles such as Giallo Siena, Brecce Medicee and Portoro. Various examples could be found in Italy and Europe, even in the Baroque period. In Rome it was used inside several churches such as, San Pietro in Vincoli, San Silvestro in Capite, San Paolo, San Giovanni in Laterano and San Lorenzo.

At the beginning of the 19th century, exports to Europe began, firstly to France, Belgium and Switzerland to adorn their castles and palaces such as Versailles, Marly and Compiegne. Later on exports to the United States of America began: the large projection room of Paramount Studios is coated with this beautiful ‘black and gold marble’.

Credits of some pictures: James St. John, Roll Stone e Vengomatto, from Flickr and Wikipedia, shared with licenses CC BY 2.0, CC BY-SA 2.0 e CC BY-SA 3.0