He developed a spa around a source of pure, hot water discovered accidentally while exploring for coal deposits.

[6] In 1874, as a member of the General Guard and Deputy Forest Inspector at Longuyon, he obtained permission to reside at Longwy, where he married Louise Legendre.

[4][5] Pierre Louis Giraud (1802–69) owned a blast furnace in Lasauvage, Luxembourg, and another in Longwy-Bas (Lower Longwy).

[5] Legendre died in 1870 and was succeeded by Joseph Raty (1810–78), clerk-factor of the Lasauvage works, who became the proxyholder in charge of the company.

[12] De Saintignon's company built three modern blast furnaces in Longwy-Bas, specializing in cast iron production.

[5] By 1913 De Saintignon et Cie had 500 workers and employees and produced 173,000 tons of cast iron annually.

[13] Fernand de Saintignon was on the management committee of the Comité des forges, the French steelmakers' association, from 1881.

He was interested in finding a prolongation of the Saar basin, and played a role in discovery of the mines of the Pas-de-Calais.

[15] When undertaking exploratory drilling for coal in 1907, at a depth of 353 metres (1,158 ft) a source of very pure water was found that gushes into the open air at a temperature of 24 °C (75 °F).

The Hôtel des Curistes was inaugurated on 3 August 1914, the day before the start of World War I (1914–18), which forced the company to close.