How Much is a Medium / Large Adamantine Box Worth?

Say you had a 5x5x5 box of Adamantine to hold something valuable (either to prevent others from getting in or to prevent whatever's inside from getting out).

How much do you think that would be worth?

How about if it was 10x10x10, big enough for a Large creature? How much would that be worth?

Basically looking for something more secure than "just" steel.

You are probably not going to get any kind of official answer. I would estimate that the cost per pound for adamantine is somewhere around 300 gold. Keep in mind that even though adamantine is very strong the walls will need to be pretty thick or it will not have enough structural integrity to function.

If you want something more secure than steel use magic. It will probably be a lot easier to obtain and cost less.

Your 5 footer will weigh in at around 4000 pounds, so assuming finished material costs will be much less than the more intricate work required to make armor or weapons, you are still talking in the range of 300,000gp. This is assuming you can find a source of 2 tons of adamantine to make it.

If you do so a godling will of course take it from you to armor his minions.

You see this kind of thing in rookie GM mistakes, easily corrected by GM fiat, "Just say no to game breaking foolishness."

@Mysterius Stranger You're right, 300 gp is exactly what Ultimate Equipment gives as the price of 1 lb of adamantine .

There is another source we can use. In one of the Adventure Paths there's an adamantine container in a from of a big scroll tube (judging by the illustation, about 1.5 long and 6 inches in in diamater). It additionaly posses a complex combination lock. If forced open, and therfore no more able to serve as a secure container, it is described to be worth 200 gp as a curiosity. Assuming all of it to be the price of adamantine, we'd get 200 gp for approximately 2.75 square feet of adamantine plates.

5x5x5 cube has a surface area of 150 square feet, so that would make it worth approximately 10900 gp. 10x10x10 cube has a surface area four times as much, so that would make it approximately 43600 gp.

As Mysterious Stranger pointed out, such big boxes may need thicker walls, so the price would increase. On the other side, if in the original item the value added to the price of adamantine is significant, the result would be lower.

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I would add that the price of adamntine in that AP doesn't much with the price of adamantine in UE. With 200 gp worth of adamantine (0.67 lb), assuming that it's density is comparable with that of iron (0.28 lb/cubic inch) you wouldn't be able to make a container as big as depicted in the AP, unless it's walls were 0.005 inch thick, which is impossible.

Use the secret chest spell

Uhmm, have you considered the cost of an item made from adamantine might well include the cost to actually work the material. I will stop promoting silliness now.

Ok, one more bit of silliness, have you ever wondered what Adam Ant and Atom Ant were trying to tell us with there choice of names?

Odd, I got an error message that my response could not be parsed, but the post went in anyway. Have fun debugging if it is necessary.

Adamantine doesn't state that it weighs more or less then normal metal (compared to something like mithril which weighs less). Looking at the equipment guide we can see that a medium chest weighs 50 lbs and large chest weighs 100 lbs. However, these chests are made primarily out of wood.

mild steel has a density of 7.85 g/cm3 and oak has a density of 0.85 g/cm3 which means that all things being equal a wall made out of mild steel weighs a little over 9 times more then an equivalent oak wall.

doing a straight conversion we can take the weight of the chest, multiply it by the weight of steel/adamantine multiplied by the cost gives us how much an equivalent adamantine chest would cost.

50x9.2x300 = 138,000gp

If we assume that the stats for the chest simply represent how many HP one wall of the chest has (since you wouldn't need to break more then one wall to get inside) we see that a medium chest has 15 hitpoints which is equivalent to 1 1/2 inches of wood. At the same thickness our adamantine chest has 60 hitpoints. In theory you could get away with half the thickness which leaves you with 30 hitpoints, and a cost of 69,000gp. You could reduce it's thickness again, leaving you at 15 hitpoints as per the original chest (which we will assume is the structural minimum) leaving your cost at 34,500gp and a chest that weighs 115 lbs. The only advantage it has over a normal chest at this point is it's increased hardness value and probably an enhanced break DC.

A large chest has a wall that is approximately 3 inches thick and weighs twice as much as a medium box. So, its cost would be double

100x9.2x300 = 276,000gp and 120 hp

at 1/4 thickness = 69,000 and 30 hp

This of course is just the cost of the raw materials. This would get added to the item's base price and you might as well upgrade the lock to something nicer then simple. Otherwise you're left with a really expensive box that can be picked by beating a DC 10.

Whatever the GM says it's worth.

If you want something more secure than steel use magic. It will probably be a lot easier to obtain and cost less.

Elaborate?

Use the secret chest spell

Won't work in this case.

Whatever the GM says it's worth.

Well, I am the GM here.

It's entirely possible/likely I just made a big mistake and the best route forward is to just say "We're just going to pretend it was steel the whole time." But I'm seeing if I can roll with it.

For example:

"100x9.2x300 = 276,000gp and 120 hp"

If we assume Steel costs like 1 GP a pound, that means a steel box of that size is still 920 gold. For a 10x10x10 cube.

For comparison, apparently an entire Bank costs <1,600 gold.

Even dropping Steel to 0.5 gold a pound still means this 10x10x10 cube is about 25% the cost of an entire bank.

You can just have an area "enchantment" causing that metal to be adamantine while in the area, but return to mere steel when removed from that area. It is a variant of an old Arduin standard to stop us from mining golems. The issue has been around for nearly as long as there has been gaming.

Ok, umm...yeah. Lets do a quick and dirty GM cheat for something reasonable.

Instead of making a cage out of Adamantine, lets have an Iron cage fortified with magic to make it equal to a Forcecage spell. The cage has a separately paid for lock on it. I'm going to assume the price of the cage in the casting of the spell since this could of just been a forcecage and we're only using the iron bars as a gimmick to make the forcecage something that can be opened and locked via disable device.

Casting Forcecage is 7x13x10gp= 910gp+500gp material cost. Making said Forcecage permanent adds 7,500gp. Total cost is 8,910gp. Size is anywhere from 20' cube to any desired size as long as its smaller. Size can't be changed once created. The force effect 'coats' the iron cage. The gaps between the bars aren't covered in force effect (or are, creator's choice). Hardness 30 and 260hp for the force effect. If somehthing does that much damage the entire spell effect is dispelled and the iron cage is all that remains. The cage can have its HP restored by any caster casting Forcecage on it. That will only restore its HP it won't allow the cage to gain more than it was initially created with.

I'd highly recommend an expensive normal, or even a magical lock be placed on this cage.

Standard Forcecage is immovable, but there's a mention of a possibility of anchoring the forcecage to a ship, so a movable forcecage should be possible. I'm not sure though, should that incrase the price.

Let's use shields as a good stand-in for walls. While there aren't rules for adamantine shields (sadly), let's use the UE benchmark of 300gp/lb as a good example. A light steel shield for a medium-sized creature weighs 6 lbs, 1 lb more than a wooden one (and let's not bring real-world physics into this if we can help it, please). 4 light steel shields welded together makes a fairly convincing 5' square steel wall, and weighs 24 lbs. 24 x 6 (for a cube) is 144 lbs. (144 lb x 300gp/lb) + (24 shields x 9gp/shield) = 43,416gp for such an impregnable box. Throw an extra 1 or 2 thousand for a suitable door or locking mechanism, and you've got a very reasonable 45k gp for an adamantine safe.

But seriously, don't make a safe out of adamantine, adamantine is vulnerable to rust. Actually, if your admantine shields are actually +1 adamantine impervious light steel shields (I'm pretty sure that's what you call these), that changes the cost per shield from 1809gp to 5809gp. Ouch!. That bumps the cost to 139,416gp (before your hinge and locking mechanism). Really only store stuff in there that you absolutely couldn't put anywhere else.

There is a cheaper alternative, however. Make a smaller safe out of 6 light steel shields made out of sunsilver. 1 of these is 309gp, and so 6 of them are 1,854gp for a, let's say, a 2.5' cuft box. There's still the problem of sunsilver being too soft to withstand adamantine weapons (hardness 8), but that's where fortifying stones come in. Because this box does weigh less than 100 lbs, you can attach three of these stones to the inside of the box, which bumps the hardness to 23 and the cost to 4,854gp (the entry for the stones does say that you could affix multiples to same object). Throw in some cash for a hinge and a lock, let's put it at 7,000gp total. Very doable. Kill whoever you want to stuff in there, trap them in a soul gem, and stuff their corpse into an anoxic bag of holding, and you should be set.

It's entirely possible/likely I just made a big mistake and the best route forward is to just say "We're just going to pretend it was steel the whole time." But I'm seeing if I can roll with it.

For example:

"100x9.2x300 = 276,000gp and 120 hp"

If we assume Steel costs like 1 GP a pound, that means a steel box of that size is still 920 gold. For a 10x10x10 cube.

For comparison, apparently an entire Bank costs <1,600 gold.

Even dropping Steel to 0.5 gold a pound still means this 10x10x10 cube is about 25% the cost of an entire bank.

It should be noted that a bank vault for medieval technology isn't made of steel (nor is any other large structure); casting that kind of a steel structure was a roughly 1900's innovation. It's just a room with thick walls (likely stone). Modern vaults primary construction is in fact mostly high strength concrete ( https://en.wikipedia.org/wiki/Bank_vault )

blahpers wrote:

Whatever the GM says it's worth.

Well, I am the GM here.

Well then, Q.E.D.