[RPG] the most expensive material in the world that could be used to create Pun-Pun’s lute

Black, pure, abyssal bloodiron, strung with a dragon's vocal cords and demilich teeth (~44,000 gp)

I'm starting with the following assumptions:

1. Pun-Pun can only exist in D&D 3.0/3.5, so only materials detailed in that edition qualify.
2. We're only interested in the most expensive material, per pound, which could feasibly be used to build a lute, and will ignore other factors which would increase the lute's value, such as exceptional craftsmanship, historical importance, or magical enhancement.
3. No priceless materials. A material must have a defined price to be expensive.
4. Based on the question's mention of adamantium and platinum, we should assume that it's possible for Pun-Pun to craft a fully working lute out of any material, despite that instrument ordinarily being made of wood.
5. As per Complete Warrior p.136, a particular object can be made of only one special material. No silvered adamantine.

Using the Giant in the Playground Special Materials Index as a reference, the most expensive I can find are abyssal bloodiron (Planar Handbook p.69) and thinaun (Complete Warrior p.136), which both cost at least 10,000 gp for a weapon, or 3⅓ the price of adamantine.

Thinaun costs 10,000 gp for a light weapon (ranging from 1 - 4 lbs) and 15,000 gp for a one-handed weapon (3 - 8 lbs), so at first glance it's more expensive than abyssal bloodiron, which is 10,000 gp tops. However, lets remember one thing: Pun-pun the kobold is a Small creature, and a lute sized for him weighs a quarter of normal.

That's ¾ lb for a wooden instrument. Now, if you just polymorphed that from wood into steel, it would become approximately twelve times heavier and weigh 9 lbs, but the acoustics would be all wrong. A functional lute is sounded by the ability of the strings to resonate the body. That's why lutes are normally made from a light material like wood. The lute has to be made of thin enough metal to weigh something much closer to 1 lb, so we're unlikely to need 15,000 gp worth of thinaun.

So thinaun and abyssal bloodiron are both 10,000 gp for a weapon, but abyssal bloodiron also increases the cost of magical enhancements by 2,000 gp. While we're not counting the price of enhancements in the overall material value, it's a given that this lute either has been enhanced, or soon will be by whichever adventuring bard acquires this most legendary item.

By this tiebreaker, abyssal bloodiron is the most expensive special metal. It's more expensive than adamantine (3,000 gp for a weapon), obdurium (twice that, at 6,000 gp), Oerthblood (6,000 gp) and stygian ice (6,000 gp per weapon, 2,000 gp per pound). It's more expensive than starmetal, which as per Complete Arcane costs 5,000 gp per weapon. And while riverine (Stormwrack) is extremely expensive, it's still no more than twice the price of adamantine for any given use.

Aside: Why not gemstone?

For the previously mentioned reasons of acoustics, I don't believe that diamond or gemstone has the right material properties to make a working lute, at least not one that anyone but the superhuman Pun-Pun can play. Gemstone is generally too hard to vibrate and the sound response would be poor. We also don't know what size a diamond is, so it's impossible to price.

However, in Into the Wormcrawl Fissure (Dungeon #134, p. 85), there is a single star sapphire the size of a fist worth 12,000 gp. The specific density of sapphire is about 4 g/cm³, meaning that even if you did produce an instrument from this gem (which would ruin the visual qualities of cut and clarity that gems are generally valued for), a 10cm cube of sapphire weighs 4kg, or 8.8 lbs, giving this sapphire a value of only 1,364 per pound.

But if we're trashing priceless gemstones, lets go all the way and scrap a chaos diamond (DMG p.252), a one-pound gem the size of a fist and costing 160,000 gp. At this point, however, we have to stop, because, firstly, we could trivially use epic-level adamantine bracers of relentless might (4,384,000 gp for 1 lb) or even an infinite value of epic items.

Secondly, as I've mentioned, I do not believe any normal person could reasonably play a solid diamond lute.

But we can make it even more expensive.

Dragon #347, p. 47 describes pure ore, a variant type of ore of exceptional purity found on the Plane of Earth. Using as little as one ounce of pure iron ore is sufficient, and increases the cost by 400 gp per lb, or 80% the price of mithral. Abyssal bloodiron is, as the name suggests, a carefully smelted alloy of extraplanar iron and blood. Crafting an item from this material should pose no challenge to Pun-Pun.

However, abyssal bloodiron has this ugly red tint to the edges, and that's not to everyone's taste. That's why we use colored metal (Races of the Dragon p.122), a kobold crafting tradition which uses trace minerals to change the hue of metal. Doing so increases the price of an item by 10% to 25%.

Depending how many pounds of metal make one light weapon (I'm assuming between 1 and 3) and the price of coloring, we're looking at between about 4,100 and 13,000 per pound.

I'm omitting the possibility of alloying with Oerthblood (Dragon #351 p.45, +6,000 gp per weapon), as it's described that weapons "must be made of a specific alloy", suggesting that this is a material rather than an additive like pure and coloring, and I'm also assuming that even if you had sufficient metallurgy skill, you'd essentially be making half oerthblood and half abyssal bloodiron, which would only dilute the price.

I'm also ignoring pandemonic silver coating (Complete Warrior p.136, +9,000 per weapon), as the same page notes you can't make an item of multiple special materials, and I feel like this qualifies; but also importantly, pandemonic silver has the properties of alchemical silver, and DMG p. 285 is clear that the alchemical silvering process doesn't work on rare metals; it also only works on steel, and abyssal bloodiron is strictly speaking a form of cold iron. You could arguably apply it to thinaun, which is a steel alloy, but again I'm not counting this, as I feel it's against the spirit of the no multiple special materials rule.

But we're not done yet! A lute needs strings: dragonsong strings (Dragon #332, p. 52-54), crafted from the vocal cords of a gargantuan dragon, costs an additional 18,000 gp. This is quite possibly the most expensive component of the entire instrument. This isn't a magical enhancement, so it fully counts as a material component.

Is there any way to make it more expensive?

User ShadowKras notes that other power components made of other dragon body parts (Dragon #332, p. 56) have a market price. If any of these can be used as part of a lute, and weigh more than their equivalent in abyssal bloodiron or thinaun, they would increase the instrument's price significantly.

• Horn of an adult force dragon (42,200 gp): A gargantuan dragon has a standing height of around 16 feet (Draconomicon), so at a conservative estimate its horn might be two feet long and 6 inches wide at the base, which assuming a perfect cone of solid keratin is about 226 cubic inches volume giving us just under 5kg (11 lbs) of horn, amounting to 3,836 gp per pound. Three pounds would cost 11,508 gp, making this a close contender to black pure abyssal bloodiron (11,440 to 13,000 gp for one light weapon), but the margins are too close to call.
• Fire-breathing dragon teeth (220 gp): Since this works for any size of dragon, one could easily use four full wyrmling teeth as tuning pegs. Four real-world guitar tuning pegs weigh about one-tenth of a pound, giving us a value of 8,800 gp per pound and allowing us to increase the item's price by 880 gp.
• Demilich soul gems (40,000 gp): If we want to be ridiculous, we can instead craft our four tuning pegs from the soul gems a demilich uses as teeth (Dragon #317, p.47). Eight soul gems have a value of 40,000 gp, allowing us to craft our four tents to add a value of 20,000 gp.
• Other dragon parts don't make much sense as part of a lute (a dragon heart might make an excellent bagpipe or drumskin, but not a lute) or are too large to be worth much pound-per-pound. A prismatic dragon skull is worth 22,500 gp, but even a wyrmling prismatic dragon is Huge, so its skull might equal that of a T-Rex, weighing around 2,500 pounds (and while that's a figure for a real-world stone fossil, bone has a a similar densities), making it very cheap per pound of material.

Pun-Pun could, if he wished, make an even larger lute, and with epic checks no doubt even play an instrument too large for him to reach the strings (as a free action, while balancing on a cloud, etc). Once it begins to weigh as much as a one-handed weapon, it's definitively more valuable to switch to thinaun. Since thinaun is likewise a steel alloy, all of the above enhancements would equally apply. In fact, if you don't feel like visiting the Blood War to mine abyssal iron, and don't intend to magically enhance the instrument, thinaun would be evenly priced even for a small instrument.

The exact price of abyssal bloodiron and weight of a functional lute made from metal are not specified, so we can't easily pin down the price for the finished item. What we can say with certainty is that it's made from the most expensive material.