I write all my stuff down with a quill on parchment. I know in this time we have paper, pens, pencils, computers, software but I prefer to do it the old way.
When I saw a page of Mozart's Requiem at his former house in Vienna I fell in love with it and since then I do it that way. I know that for instance Bach's compositions are showing ink corrosion and Rembrandt for instance used Irongall ink as well, but still it is sooooo beautiful.
Nowwww to get back to the question, on what and with what do you write down your compositions?