Hi Parker,
I assume you're talking about "cold-pressed hammers," or hammers that need some kind of chemical hardener to produce a good tone. (Such as Steinway hammers or Bacon-felt hammers.) I would not use chemical hardeners on "hot-pressed hammers," or hammers that are designed specifically to not need chemical hardeners to get good tone. (Such as Renner Blue Points, Yamahas, etc.) There are different ways to bring up the tone in those ones as needed.
With that said, the benefit of what you're describing (side lacquering) is that you can do different strengths of mixtures in different areas. Full strength under the strike point and half strength under the shoulders if you want. You can "bring them up" easier the first time around with not as much needling work to do. (In theory.)
Dunking the hammers typically requires more needling to "bring them down," and some people prefer that process. It's more work, but it could be faster. I think it comes down largely to individual preference and the methods individual technicians are taught.
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Benjamin Sanchez, RPT
Piano Technician / Artisan
(256) 947-9999
www.professional-piano-services.com------------------------------