Titanium is 4.51 g/cm³, vs osmium at 22.5 g/cm³. Did you mean tungsten at 19.3 g/cm³?

Midwest Tungsten sells a 1.5" cube (1 kg) for $200. I have one, as well as a magnesium cube of the same size. They look identical but the Mg cube weighs 1/10 as much. It's fun to let someone hold the W cube to feel the weight and then toss them the Mg cube with "Here, catch!"

https://shop.tungsten.com/tungsten-cube/

I want that 7" cube, but $35k is well out of my price range.

Where'd you get the magnesium cube?

Not sure where they got it from, but the same folk have https://shop.tungsten.com/magnesium-cube/

I have both too! It’s a really fun talking piece when I have friends over.

Broken tungsten carbide drill bits are a much cheaper way to get dense weights (I made a running vest one time) if you can find a machine shop or online, etc.

This is the HN comment I didn't know I needed.

Yes, tungsten. Oops

If you just used lead the billet would be 31lb, it'd be procurable and shippable for under $100.

Osmium is about twice as dense so yeah that would still be shippable at around 60 lb... I don't think that's even tens of thousands at that point? Isn't it going to be in the millions? I'm just thinking that like if you went for gold instead, 50 lb is 800 oz, at $3300/oz these days doing this with gold is $2.64M, no? And surely osmium blows gold out of the water by like 10x, right?

Jokes on you when the $100 of insurance is all you get back from the post office...

Edit: a sibling comment points out that you can probably do this under $100 with tungsten too and get up into that 50lb+ range.

Depleted uranium would be my first choice for this; we had big bars of the stuff laying around the lab that we used for door stops. (The lab was a place that designed nuclear weapons.)

DU is harmless unless you eat or breathe it but alas it's now illegal to possess more than a minute quantity of it.

Tungsten is actually slightly denser and it has the advantage of being obtainable.

Isn't DU heavy metal-dangerous, but not radiation-dangerous?

Yes

It's both. DU is never completely "depleted" because radiation falloff is asymptotic. DU is primarily an alpha emitter and alpha particles cannot penetrate skin, but they can cause damage if you breathe, eat, or inject DU dust.

That's why our use of big lumps of DU as door stops was considered "safe" (at that time several years ago) but in labs where people machined the stuff they were a lot more careful.

Sorry to be a downer, it’s a fun thought experiment – but also a good way to get a postal worker hurt, and possibly a nice lawsuit :)

How? Postal workers shouldn;t be carrying things that are too heavy. I suspect the USPS would have to arrange a special delivery.