CAUT

It is part number

7726  LACQUER - HAMMER VOICING SOLUTION PRE-MIXED (SHIPPED FROM SUPPLIER) 

Available from Steinway Parts

BTW, I would highly recommend pouring a bit of whatever lacquer you are thinking of using into a flat-bottomed polyethylene container and letting it fully dry. I did this with the Wurdack lacquer and the Rudd lacquer that I've been using (Rudd was recommended as a local supplier of very high-quality lacquer). The resulting films were quite different. The Wurdack is tough and flexible, the Rudd is brittle.

So, though Horace has quite nicely shown that you can get good results with many different hardeners if your ears are looking for the right sound, the process may take longer or shorter, and be more or less durable depending on what you use.

I am currently working with Wurdack lacquer, but not straight from the can. I filled the bottle for my kit from the Wurdack can, then poured it into the container mentioned above and let it fully dry. Then I stuffed it back into the bottle and filled with acetone. The lacquer thinner is really not very nice stuff, and is very strong-smelling. The acetone is relatively benign, and will dry MUCH faster. The result seems the same in the hammers.

Doug