why president of america uses multiple pens to sign a bill?

recently obama used 22 pens to sign a bill (2010 Patient Protection and Affordable Care Act) though when i first heard of it muliple ideas floated in my mind first i thought each pen contains different inks or chemicals so that others cant fake his signature, second thought was using multiple pens with different color inks signature might look colorful, and other thoughts was he might keep many pens because he dont want to miss to sign the bill because of failure of one pen :)

but i was really amazed to know that it was a obscure washington tradition  and practice that stretches as far as franklin roosevelt and the idea behind it is very simple the pens used to sign a historic legislation itself becomes a historical artifact and more pens he uses more the persons he can offer and its a kind of thanks giving for the people who helped to create that piece of history and it is said that white house often engraves the pen and given to the supporters or proponents of the newly signed legislation.

It said that Lyndon Johnson signed civil rights act in 1964 with 75 pens and gave the first one to Martin Luther jr but not all the presidents uses multiple pens President George w.Bush  always preffered to use one pen and other unused pens was gifted as the souvenirs.

So what happens to these pens? though some of these pens make its way to museums others becomes proud display or show peice in recipients home or offices so what ever it is though this pen culture is taking place from long time this is the first time it made into media's attention see the above video for insight on how it is done that obamas latest signature on bill was not done in single shot but with  multiple breaks