Steelpushing on metalminds?

[Ink and Embers Any pronouns]

In Bands of Mourning, we see that it's impossible to allomatically Push (and presumably also Pull) on metalminds, which is

Spoiler

how they identified the Bands to begin with, thinking they were aluminium. This seems to be a relatively well-known fact about metalminds, as the characters conclude they've found the Bands fairly quickly.

However, at the end of the Well of Ascension, Marsh attacks Sazed by Pushing Sazed's bag of metalminds into him, meaning he's able to heal using gold.

Why? Is it because Marsh was using Hemalurgy that he was able to Push on metalminds? Is it a special property of the Bands? Is it something else?

(As an aside, the reason I initially joined the Shard was to ask this, and I have consistently forgotten to do so for eleven months.)

[Returned he/him]

We've known it's possible to push on metalminds since The Final Empire-- we saw Vin do it to Rashek's bracers (which were even harder to push due to their piercing his skin). It comes down to Invested objects resisting being affected by other Investiture, and a more Invested object resists more and so takes more strength to affect.

The Bands of Mourning were extremely Invested (well, before they were drained at least) and so they would take a lot of strength to affect. Far more than an everyday era 2 Allomancer could muster, apparently. Sazed's metalminds were very small (you're referring to the bag of rings, I think?) and so would hold far less Investiture, even when full, than the Bands did. Marsh was a more concentratedly powerful Allomancer (as all were in era 1) and also may have had enhanced steel Allomancy (I don't recall if we know how many relevant spikes he had, but we know you can stack Allomantic power by adding more) and may have had some of Ruin's own power to draw on (though I think that latter possibility is pretty shaky).

So, Wax's maximum Allomantic strength was less than Marsh's, possibly far less, while he also had far more Investiture resisting his efforts than Marsh did.

[Aeoryi she/her]

Marsh's ability appears to be extremely strong when compared to the small amount of things likely stored in the metalmind to begin with; the Bands are likely filled to the brim with whatever it is that they're filled with and thus resist steelpushing more