I thought I'd migrate this into a new thread, in case there was any discussion to be had on it.
Now, necrotic steel might be onto something if you could make a mech of it and then cover the mech in magical darkness so you can have the Str bonus even during the day. But as it stands, it's got more penalties than it does advantages, and I question the pricing. In fact, I have a lot of questions for any designers who see this.
-what is this 'terrible ritual' involved in making necrotic steel that makes it automatically Evil (TM)? Do I bleed a bunch of creatures dry and quench the properly-enchanted steel in the accumulated blood? I assume there's some sort of malicious sacrifice going on.
That's a fine evil ritual idea. The intent was to not have The One True Ritual, but rather to let players and (especially) GMs run wild with their own notions here. In a book with limited space, and as much ground to cover as Steam Warriors
does, we had to prioritize which things got extensive descriptions and which ones didn't. If necrotic steel was/is on the way to becoming a core element of the setting, it would/will be more fleshed out. Pun intended.
-what effects does it have if I make weapons and armor out of this stuff? If I had to ad hoc it, I'd say necrotic steel wants to be a weapon, and gives some necromantic goodness to slashing/piercing weapons, while organic steel makes incredible armor--probably easier to wear, lighter, and very accomodating--possibly as accomodating as only a living creature can be.
As it stands, both necrotic and organic steel need to be bonded to a living being to remain viable for any length of time. They draw nourishment from living beings (in different ways, as you can imagine). Any gear that you made from them would only last a short while. More research is needed to develop viable long-term uses for them.
But we can speculate. The Strength bonuses and penalties are a given, although they wouldn't be cumulative. And you could certainly take things in the direction you outline. It fits with the traditional "evil attacks, good defends" paradigm.
Another option would be to have organic steel items take on some plant-like properties: camouflage, poison, thorns, even spores. You could come up with a host of neat armors, weapons, even miscellaneous items. If every organic steel weapon automatically did +1 piercing damage due to spines, gave the wielder a +2 Fort Save vs. poison, and allowed a +2 bonus to Hide checks, what would you have? An elf-style weapon that would also be a boon to assassins.
Ditto for necromantic steel. It could grant a +2 to all saves vs. death, along with doing +1 negative energy damage on a successful critical. Perhaps you could even feed your own HP into the weapon to raise the crit damage.
Really, you could do all kinds of cool stuff with this, particularly once you get into making magic items or steam power combinations.
-why are these substances so expensive? The bonuses they give aren't that spectacular. They're very cool materials, yes, but last time I checked, 'cool' didn't add onto the price tag, and there's not really much of a way to use them.
Consider that they're in limited supply. Scarcity always drives up price; you should see what fresh tomatoes sell for in Edge.
Also, remember that these special metals grant steamborgs a bonus on their Lose Self checks. Admittedly, necrotic steel has its own penalties, but not everyone will consider those a problem. If your party wants to make life a little easier for their near-robotic steamborg tank, they'll probably be glad to pony up the gold for organic steel. If the nefarious cleric you crossed wants revenge, maybe she'll pay to have necrotic parts installed the next time you go in for an upgrade. They might be worth the cost in story value alone.