Is Snape an Alchemist?

[Tonks]

No: HPFGUIDX 156628

We know that DD was an alchemist because he worked with Flamel. We know 
that Snape is a potions genius.  We know that Snape is the person that 
DD wants when some serious potion making is called for. So here is a 
question for people to discuss. (I hope.) 

Is Snape an Alchemist and if so what does this mean for book 7? What 
has he done for LV?  What does he know that LV doesn't know that he 
knows?  How does it affect Harry?

Tonks_op