I have suffered a lot of aggravation with string mutes, but today, I have had the joy and pleasure of using what is possibly the best mute ever invented for grand pianos. It's this gizmo right here, a split mute from Supply88 which I came across quite randomly in a discussion with @twocats.

What is so amazing about this? I'm going to try to be mildly coherent here:
- It's one mute for grand pianos that solves everything.
- You don't need a separate felt mute for copper wound strings and rubber mutes for steel strings.
- You can mute every string combination that you need -- outer strings, left strings, right strings. It does it all with a single mute.
- It's custom made with some interesting materials that I have never seen employed in mutes before. Handle seems to be 3D printed. There were some minor threads I trimmed for appearance but causes no issue.
- It's very easy and convenient to slip between the strings... the material is just perfect and tough too.
- It's a great shape, large so that it won't fall between the strings, but easy to manipulate at the same time.
- It seems like it will last a long time. It won't get gross like a felt mute.
Quoting from the website, everything is on point:
This is the ultimate grand mute, allowing any combination of strings in a bicord or tricord unison to be quickly muted or unmuted.
- Durable polyurethane outlasts felt or rubber mutes
- Does not discolor copper strings
- Does not dry out like rubber
- Does not absorb dirt like felt (can be cleaned if discolored by dirt or rust)
- Soft, flexible elastomerized polyurethane material
- Lighter than felt or rubber
Could I be exaggerating? I don't think so... I have possibly over half a dozen of different mute designs and this one has floored me. It has replaced my previous favorite, which is very closely related in design, but which is no longer manufactured. There's a lot of thought that went into this design and construction.
I would consider this a must-have in every tuner's toolkit. I'm definitely going to purchase a spare.
Well done, Supply88!