In short, I expect to look primarily at the effect of the special material and build from there.
A few of the common materials from the PRD, first quoting the PRD and then giving my take on them.
In almost all cases, I disregard part of the description: almost all ‘metal materials’ are actually alloys rather than pure materials. This lets me treat them as justification for various qualities at different grades, and even allows me to mix them somewhat.
Bypassing DR/material is usually more or less free — the target has a benefit that renders them less harmed by everything except this material, so this material bypassing that is not inherent in the material and shouldn’t be paid for. Actually, I’d be willing to consider a quality that directly targets and adds damage in these cases: an item made of special silver doesn’t just bypass DR/silver, it does additional damage (as with flaming or bane… not sure which, I could go either way).
Mined from rocks that fell from the heavens, this ultrahard metal adds to the quality of a weapon or suit of armor. Weapons fashioned from adamantine have a natural ability to bypass hardness when sundering weapons or attacking objects, ignoring hardness less than 20. Armor made from adamantine grants its wearer damage reduction of 1/— if it’s light armor, 2/— if it’s medium armor, and 3/— if it’s heavy armor. Adamantine is so costly that weapons and armor made from it are always of masterwork quality; the masterwork cost is included in the prices given below. Thus, adamantine weapons and ammunition have a +1 enhancement bonus on attack rolls, and the armor check penalty of adamantine armor is lessened by 1 compared to ordinary armor of its type. Items without metal parts cannot be made from adamantine. An arrow could be made of adamantine, but a quarterstaff could not.
Weapons and armor normally made of steel that are made of adamantine have one-third more hit points than normal. Adamantine has 40 hit points per inch of thickness and hardness 20.
Type of Adamantine Item Item Price Modifier Ammunition +60 gp per item Light armor +5,000 gp Medium armor +10,000 gp Heavy armor +15,000 gp Weapon +3,000 gp
So… weapons gain hardness 20 (from the default of steel’s hardness 10) and bypasses DR/adamantine (which is uncommon). Armor gains DR 1/— if light, DR 2/— if medium, or DR 3/— if heavy. Per RAW they’re all masterwork but the price is included.
I’m going to reduce this to basics:
- The impervious perk increases an item’s hardness by 5. I’m willing to let that be repeated, and since perks are considered grade 1 qualities I’m willing to have impervious have multiple grades: hardness is increased by 5 per grade. Adamantine has a hardness of 20, 10 higher than steel, so this would be a grade 2 quality.
- The rugged quality from Green Ronin’s Black Company masterworks rules is +2 hardness and break DC per grade. I don’t think hardness 20 is worth quite that much here, so I’ll stick with the impervious perk.
- The durable perk doubles an items hit points… but the sturdy quality from Green Ronin’s Black Company masterworks rules is +50% per grade. I think I like that better, so I’ll be dropping the ‘durable’ perk. An adamantine weapon or armor has a third more hit points than usual (but double the hit points per inch thickness, strange), so I’ll call that one grade and make it a bit better at 50% more hit points.
- DR/— from armor is one grade per point of DR. There could reasonably be a surcharge or limitation of some sort of for light and medium armor, but I’m not going to bother yet. In any case, DR/— is handled.
The effects of a weapon made of an adamantine alloy are “+50% hit points, +10 hardness”: a grade 1 quality and a grade 2 quality. In a weapon with no other qualities, this adds 4,500 gp to the market price of the item. Unlike RAW, this is not a ‘masterwork item’ (no +1 enhancement bonus to hit).
If I wanted to be fiercer about it, I could say that adamantine construction is itself a grade 3 quality… but I won’t do that today.
Adamantine armor is pretty simple. Like weapons the hit points and hardness are increased, and the armor grants DR/—.
- Light armor gains hardness 20 and 50% more hit points, and DR 1/—. This amounts to one grade 2 quality and two grade 1 qualities, a total of four grades. This adds 4,000 gp to the market price (4*4*500 gp = 8,000 gp, halved because this is armor).
- Medium armor gains hardness 20 and 50% more hit points, and DR 2/—. Two grade 2 qualities and one grade 1 quality, a total of five grades. This adds 6,250 gp to the market price (5*5*500 gp = 12,500 gp, halved because this is armor).
- Heavy armor gains hardness 20 and 50% more hit points, and DR 3/—. A grade 3 quality, a grade 2 quality, and a grade 1 quality, a total of six grades. This adds 9,000 gp to the market price (6*6*500 gp = 18,000 gp, halved because this is armor).
The armor is generally lighter than RAW because the costs are halved, but unlike RAW these will make following qualities more expensive… by quite a bit, really.
Mithral is a rare, silvery metal that is lighter than steel but just as hard. When worked like steel, it can be used to create amazing armor, and is occasionally used for other items as well. Most mithral armors are one category lighter than normal for purposes of movement and other limitations. Heavy armors are treated as medium, and medium armors are treated as light, but light armors are still treated as light. This decrease does not apply to proficiency in wearing the armor. A character wearing mithral full plate must be proficient in wearing heavy armor to avoid adding the armor’s check penalty on all his attack rolls and skill checks that involve moving. Spell failure chances for armors and shields made from mithral are decreased by 10%, maximum Dexterity bonuses are increased by 2, and armor check penalties are decreased by 3 (to a minimum of 0).
An item made from mithral weighs half as much as the same item made from other metals. In the case of weapons, this lighter weight does not change a weapon’s size category or the ease with which it can be wielded (whether it is light, one-handed, or two-handed). Items not primarily of metal are not meaningfully affected by being partially made of mithral. (A longsword can be a mithral weapon, while a quarterstaff cannot.) Mithral weapons count as silver for the purpose of overcoming damage reduction.
Weapons and armors fashioned from mithral are always masterwork items as well; the masterwork cost is included in the prices given below.
Mithral has 30 hit points per inch of thickness and hardness 15.
Type of Mithral Item Item Price Modifier Light armor +1,000 gp Medium armor +4,000 gp Heavy armor +9,000 gp Shield +1,500 gp Other items +500 gp/lb.
Mithral halves the weight of primarily metal items and increases the hardness by 5. There is no mention of an increase in hit points.
Armor has decreased spell failure chance, increased maximum Dexterity bonus to AC, and Armor check penalties are reduced by 3… this ends up being quite nice. Also, the armor is treated as one category lighter (heavy treated as medium, medium treated as light) to a minimum of light, for the purpose of mobility and other features, but not proficiency.
- The lightweight perk halves an item’s weight, and could be considered a grade 1 quality.
- The light quality from Green Ronin’s Black Company masterworks rules reduces weight by 10% per grade, but that seems too expensive for its regular effect. Reducing weight by half honestly isn’t worth a grade 5 quality. I’m going with the lightweight perk for now.
- The mastercraft quality from Green Ronin’s Black Company masterworks rules reduces armor check penalty by one per grade. I’ll go with this for now. By RAW the check penalties are reduced by 3, but I’m willing to allow this to completely negate the armor check penalties… if someone is willing to invest that much, I’m prepared to allow it.
- The creeping armor special ability is a +5,000 gp in RAW, and is in the +2 Armor Special Ability table. It negates the armor check penalty for Stealth checks, while the mastercraft quality applies to all relevant checks. I’m inclined to go with the mastercraft quality.
- The modifier to arcane spell failure is a little trickier, but the Magic Item Compendium from D&D 3.5 has the twilight armor quality. This +1 armor quality reduces arcane spell failure by 10%. As a +1 armor quality maps to a grade 2 quality in this system, I’m fairly comfortable considering twilight a scaling quality reducing arcane spell failure by 5% per grade. As with mastercraft above, someone could entirely negate arcane spell failure… but it gets very expensive for heavy armor (grade 8 to negate the 40% arcane spell failure of splint mail and half-plate!).
- I don’t have anything specific for increasing the maximum Dexterity bonus to AC, but since an enhancement bonus is two grades per +1 I’m willing to call this one grade per increase here. For now at least.
- The mobility advantages seem pretty mild, really. I’ll call them a grade 1 quality for now.
Given the above, to exactly model mithral weapons basically halves the weight (lightweight, grade 1) and increases hardness by 5 (impervious I, grade 1); that the weapon counts as silver for DR purposes is basically free. In the absence of other improvement, a mithral weapon adds (2*2*500 gp) 2,000 gp to a weapon’s market price. This is spot on for a longsword, more expensive for a short sword or dagger, less expensive for a great axe. Since it doesn’t really do anything, I’m okay with it.
Armor, on the other hand, gets quite a bit more expensive.
- Light armor doesn’t benefit from the reduced category, but does benefit from lightweight (grade 1), improved maximum Dexterity bonus (grade 2, +2), reduced armor check penalty (grade 2 — the only relevant armor has an ACP of -2), and reduced arcane spell failure (grade 2, 10%). This is a total of seven grades! This would thus be worth 12,250 gp (7*7*500 gp = 24,500 gp, halved because it’s armor).
- Medium and heavy armor would actually be the same: lighter category (grade 1), lightweight (grade 1), improved maximum Dexterity bonus (grade 2, +2), reduced armor check penalty (grade 3), reduced arcane spell failure (grade 2). This is a total of nine grades, and add, in the absence of other improvements, 20,250 gp (9*9*500 gp = 40,500 gp, halved because this is armor).
- A light steel shield isn’t so bad: lightweight (grade 1), reduced armor check penalty (grade 1), reduced arcane spell failure (grade 1, 5%), a total of three grades. 2,250 gp (3*3*500 gp = 4,500 gp, halved).
- A heavy steel shield is more expensive: lightweight (grade 1), reduced armor check penalty (grade 2), reduced arcane spell failure (grade 2, 10%). A total of five grades, 6,250 gp (5*5*500 gp = 12,500, halved).
Combining Special Materials
Because these are alloys rather than pure metals, it seems plausible that someone could try to blend them into an item that does more. An adamantine/mithral mix might incorporate the features of both.
A longsword made of an alloy (or pattern-welded billet of these two materials with steel) might include:
- hardness 20 (impervious, grade 2)
- +50% hit points (sturdy, grade 1)
- lightweight (grade 1)
This is a basic grade 4 item with a market price of 8,000 gp.
A suit of chainmail made of this material, though…
- hardness 20 (impervious, grade 2)
- +50% hit points (sturdy, grade 1)
- DR 2/— (grade 2)
- lighter category (grade 1)
- lightweight (grade 1)
- improved maximum Dexterity bonus (grade 2, +2)
- reduced armor check penalty (grade 3)
- reduced arcane spell failure (grade 2, 10%)
Grade 14! This adds a 49,000 gp to the market price (14*14*500 = 98,000 gp, halved). This is before adding any other qualities!
As just a suit of adamantine chainmail this would be only a grade 5 item (6,250 gp market price). As just a suit of mithral it would still be grade 10 (25,000 gp market price).
Complex alloys are expensive… but since by RAW they don’t exist at all, I’ll probably be okay with that after I get past being a bit stunned.
By looking at the effects of special materials, and how they fit into the rest of the framework, they can do some strange things to the costs. The materials themselves are largely unimportant, acting primarily as justification for crafting the items with these qualities. To be honest I’d be inclined to split some of the materials up a bit. Mithral does many things, and they don’t all apply to all wearers (the reduce arcane spell failure). Having the improved maximum Dexterity bonus a mix of material and cunning construction (rather than a fixed value whether the crafter wants it or not) could be a reasonable change as well, as might the reduced armor check penalty.
RAW, I don’t see why almost all armor isn’t made of mithral. It’s amazingly cheap for what it does, especially since the cost doesn’t scale with other improvements.
Actually, I’m pretty sure mithral is the most common special material for armor. As it should be, looking at this.