Liszt probably first met the Boisselot family in 1826, when the 15 year old prodigy
came to Marseille to give a series of concerts. Boisselot was the Erard agent in
Marseille, so he could well have supplied or tuned Liszt’s piano. Another reason
for the two men to meet was Boisselot’s activity as a publisher : Liszts « Etudes
en douze exercises » (these formed the basis for his future « Etudes d’exécution
trascendante »)were published by Boisselot in 1826.
Liszt, the 19th century piano composer who showed the closest interest in the
development of his instrument, probably followed with great interest the
development of the Boisselot factory, but we don’t have any proof of when he
first played one of their pianos. Certainly by 1844 he was promoting them in a big
way : at the end of the summer of that year, Liszt was back in Marseille for a
series of three concerts played on Boisselots pianos, prelude to a long concert
tour of Spain and Portugal that was to last a year., accompanied by Louis
Constantin and by concert grand n° 2027.
For Louis Constantin, acting as a piano technician and salesman, this was
obviously a fantastic opportunity to promote the family pianos in a country devoid
of any serious national production, and where the geographical situation of
Marseille gave them a lead over other French makers. What Pierre Erard thought
of all this is not known, but Liszt’s letter cited above, sounds very much like an
answer to a complaint from Pierre about this promotion of a rival firm.
The « many orders that Mr Boisselot’s son received » in Spain were certainly
one of the reasons that led to the creation of the Barcelona factory a few years
Concert grand 2027, after following the two men all the way to Portugal
(including a boat trip from Gibraltar to Lisbon), was given to Queen Maria II, and
is now in the Museu da musica.
To celebrate the end of this triumphal tour (and successful business enterprise),
Boisselot organized on May 4th 1845 in Marseille a great banquet  in Liszt’s
honour, in the premises of the factory. After the meal, Liszt mingled with the
workers (over 100 were present), and finally sat down at the piano : the last
notes of his fantasy on the Somnambula had hardly finished resounding when he
was carried off in triumph.
Liszt and Louis-Constantin were practically the same age and they spent a year
travelling together : the fact that Louis-Constantin’s son was named Franz and
had Liszt as a godfather is proof of the friendship that developed between them.
Many years after Louis-Constantin’s early death, Liszt kept in his study in
Weimar the piano sent to him in 1847 in Odessa (now in the Weimar museum).
The question of the influence of Liszt on Boisselot pianos is worth considering,
as Liszt mentions an extraordinary instrument being made for him in Marseille : «
my double keyboard pedal orchestral-harpsichord…. new wines need new
containers ».  Elsewhere he writes : « Ask Belloni to write to me with details of
the monster piano that Boisselot is building for me, if it is in Paris, what is
finished, what remains to be done ».
This instrument seems to be the answer to certain ideas expressed by Liszt in
1836 in his  Lettres d’un bachelier es Musique  : « New progress soon to come in
piano construction will certainly give us the various sonorities we are still missing.
Pianos with foot pedals, the claviharp, the polyplectron, and several other
unfinished instruments prove the general need for development. The expressive
keyboard of the organ will naturally lead to the creation of pianos with two or
three keyboards, finishing off the pacific conquest of the instrument ».
There is unfortunately no further trace of Liszt’s « monster Boisselot», and the
only instrument of the type described by Liszt is the Erard-Alexandre that the
composer installed in the Altenberg in 1854.
There is a distinct possibility in my opinion that the 1844 Boisselot patents for a «
piano-octavié » are linked in some way to Liszt’s dreams of a more powerful
instrument, although we have no proof of this.

Liszt’s fidelity to Boisselot pianos lasted until well  after the death of Louis-
Constantin : he asked Xavier to send a Boisselot upright to him in Rome in 1861,
on which he composed a number of major works.