Is there any difference when a movement states Rubis instead of jewels?
In 1704, Nicolas Fatio de Duiller discovered a way to drill natural rubies for use as bearings in watches. DeBeaufré subsequently produced the first watch utilizing rubies as bearings. By 1877, Edmund Fremy was producing artificail rubies from molten baths of alumina.
In 1892, Auguste Verneuil discovered a process for manufacturing synthetic stones. He published a paper on the process in 1902, using an oxyhydrogen blowpipe furnace. Verneuil's process was put into production a few years after this.
As far back as 1837, however, smaller natural rubies were melted together to form larger ones. Natural rubies are not as pure nor homogenous as synthetic ones, and this is one instance where the artificial surpasses the original in desirability. Watches prior to 1877 could be safely assumed to contain natural rubies, or 'rubis'. The term is applied to both natural and synthetic stones.
In my experience, natural rubies chip and wear more easily than synthetics. I see many old watches with worn rubies and jewel dust inside, as well as fractured ones. Once lubrication has dried up, dirt and friction can destroy pivots and jewels alike.