Cristofori, born in 1655 in what was then the Republic of Venice, was headhunted at 33 by one of the famed Medicis of Tuscany to work in Florence. There, at the dawn of the 18th century, he invented the precursor of what we call a piano.
And a little over 300 years later, Downie replicates the work of Cristofori and his successors, such as the Viennese Anton Walter and the German Christian Zell.
Before Cristofori, keyboard instruments were all variants of harpsichords: the key operated a lever which plucked a string with a plectrum (a wedge-shaped piece of quill). Hit the key hard or soft, the result was the same.
The fortepiano did what the name suggested (in Italian, the language of composition, "forte" means loud and "piano" means soft).
Downie: "Cristofori said, 'Let's put some hammers on a harpsichord and see what it sounds like'." The harder you played, the louder it got; the piano was born.
The term "fortepiano" came into use in German-speaking circles; in France and England it was "pianoforte". But these days "fortepiano" distinguishes the pre-Industrial Revolution piano from the modern one.
The sound (it's easily enough heard online) is more resonant than the harpsichord's, though some of the twanging sharpness remains because the fortepiano's hammers are hard, rather than felted.
"That was the sound people knew and when these new-fangled pianos emerged, they wanted that sound. They regarded the ideal instrument as a harpsichord that played loud and soft."
There is good reason for making these new old instruments. Many of the originals that survive are unplayable or were unthinkingly "modernised" in the 19th century. So the way most people get to hear 17th-century music as 17th-century audiences heard it is on instruments made in the 21st century.
Downie's interest in the craft was aroused as a young man when he decided he wanted a harpsichord.
"You couldn't buy one at a harpsichord shop and so I started reading up about it and got some tools and wood and put it all together. And I thought, 'That was fun; I'd better make another one'."
All these years later, there are about 30 of Downie's creations in existence, and a good deal of his time is spent in after-sales service, including tuning and restoring old instruments.
He makes more than simple facsimiles. Slavish copying is a waste of time, he says, because imitation crowds out craftsmanship. But that is not to say there is not meticulous attention to the detail of the original historical instruments. Precise plans, drawings, x-rays and measurements of string length and soundboard thicknesses are the essence of the art. Old wire is analysed and reproduced - in the 18th-century the phosphorus content was high and txhe sulphur content low.
The wood, too, must speak to the maker: it's usually spruce, mostly from northern Europe, and it's where the soul of an instrument resides.
"You listen to the way a piece sounds when you rap it," says Downie. "Some sounds dead, some really rings. Some even hisses when you rub your fingers over it, and amplifies even that sound. The wood has to be regarded as alive in some way when you are playing it."
In an age when popular music is so often created by computer programs, such old-style craftsmanship is a cheering sign.
"There will always be an appreciation of the handcrafted item," Downie says. "I don't think it will ever be a huge following, but it will always be there."
