The iconographic experience and the apparent dominance of fixed-pitch horns (in the sell of Starzer’s effects) lead us to the question of innovation versus time : There is always a delay between an innovation and the moment it will spread and get known. We can obviously expect this delay to be greater back in the XVIIIth century : news did not travel as fast as today.
Let us take the hand-stopping technique as an exemple : it was improved in the 1750’s in Dresden, Germany, but the very first known written source to mention this technique is the Essai d’instruction à l’usage de ceux qui composent pour la clarinette et le cor by Valentin Roeser, in 17641. It was shown for the first time in Paris by the horn player Rodolphe in 17652, 15 years later ; and for the first time in England by Spandau, in 17733… 23 years later. Not to mention that hand-stopping had been attempted before Hampel perfected it.
If hand-stopping took this much time to spread through Europe, we can reasonably assume it was the same for all horn innovations. Thus for instance, the Hampel-Werner Invention-Horn invented in 1754 in Dresden, must have been still a « new thing » in Vienna in the 1780’s…
As a matter of fact, « new mode Horns » are the exact terms used in a bill from the horn maker Balthas Fürst dated June 30th 1781, in Ellwangen, for the making of two crooks4.
This question of temporality alone allows us to state with reasonable certitude that Mozart and Leutgeb did not know the Cor Solo created in Paris in 1781, date of Mozart’s first horn concerto. Neither did they know the French orchestral horn developed in the 1790’s, but they probably encountered the previous version of this model, the Cor d’Anglais. However, this type of horn was mainly encountered in France and England.