Confused about Diamond Spray and Damage Reduction

[Tarondor]

The diamond spray spell from Pathfinder 24 reads as follows:

Diamond Spray wrote:

A cone of tiny, sparkling slivers as hard and sharp as fled diamonds springs from your outstretched fingers at tremendous speed. Any creature in the area of the torrent takes 1d6 points of slashing damage per caster level (maximum 10d6). These magical slivers are treated as adamantine and cold iron for the purpose of overcoming damage reduction. In addition, this spell bypasses up to 1 point of an object’s hardness per 2 caster levels (maximum 10).

The Damage Reduction rule reads:

Damage Reduction wrote:

A creature with this special quality ignores damage from most weapons and natural attacks. Wounds heal immediately, or the weapon bounces off harmlessly (in either case, the opponent knows the attack was ineffective). The creature takes normal damage from energy attacks (even nonmagical ones), spells, spell-like abilities, and supernatural abilities. A certain kind of weapon can sometimes damage the creature normally, as noted below.

So I'm confused. If spells ignore damage reduction, why does diamond spray mention it at all?

[Akerlof]

Because this spell does not do energy damage, the way Fireball or Scorching ray does, instead it does (physical) slashing damage.

So it is subject to DR but not energy resistance.

Compare:

Fireball wrote:

A fireball spell generates a searing explosion of flame that detonates with a low roar and deals 1d6 points of fire damage per caster level (maximum 10d6) to every creature within the area. Unattended objects also take this damage. The explosion creates almost no pressure.

verses

Diamond Spray wrote:

Any creature in the area of the torrent takes 1d6 points of slashing damage per caster level (maximum 10d6).

Far more spells deal energy damage, which ignores DR, than do physical damage.

Now, look at the rules for DR:

Damage Reduction (Ex or Su) wrote:

A creature with this special quality ignores damage from most weapons and natural attacks. Wounds heal immediately, or the weapon bounces off harmlessly (in either case, the opponent knows the attack was ineffective). The creature takes normal damage from energy attacks (even nonmagical ones), spells, spell-like abilities, and supernatural abilities. A certain kind of weapon can sometimes damage the creature normally, as noted below.

<edited to add rules quotes>

[Elven_Blades]

Damage reduction is against physical damage. Most spells deal energy based damage, so those spells would ignore damage suction.

This spell deals physical (slashing) damage, so damage reduction would normally apply. If the damage reduction was DRx/cold iron or DRx/adamantium, then this spell with bypass it (since it says the spell counts as both of those material types). Against DRx/-, the damage resistance will apply (also silver, bludgeoning, and piercing).

[Tarondor]

While all that makes sense, it's not the Rules As Written. "The creature takes normal damage from energy attacks (even nonmagical ones), spells, spell-like abilities," etc. It says "spells", not "spells that do energy damage".

That seems pretty clear. This is a spell. The creature takes normal damage from it. DR doesn't enter the picture.

[Skylancer4]

Actually that could be read as energy attacks, spells, spell like abilities to save word count instead of spelling out 'energy' multiple times. You placed the bolding where you wanted it to make your point.

That is if you want to ignore the fact that specific rules trump general rules and the spell states DR comes into play. RAW.

[kingpin]

Before I looked at it I was expecting to see it had no SR and make a comment that it must work similar to pellet blast. But this just seems to be an exception to the rule.

[Starbuck_II]

kingpin wrote:

Before I looked at it I was expecting to see it had no SR and make a comment that it must work similar to pellet blast. But this just seems to be an exception to the rule.

Agreed it should be either SR no or not be affected by DR.

[kingpin]

The reason for that in pellet blast is easy, it is a conjuration so those balls of metal are actually real.

Diamond Spray is an evocation which although it is about creating something out of nothing, it almost always still energy related. This seems to be an exception.

[Mucronis]

Damage Reduction: How does DR interact with magical effects that deal bludgeoning, piercing, or slashing damage?

Although the Bestiary definition of Damage Reduction (page 299) says "The creature takes normal damage from energy attacks (even nonmagical ones), spells, spell-like abilities, and supernatural abilities," that's actually just referring to damage that isn't specifically called out as being of a particular type, such as fire damage or piercing damage. In other words, DR doesn't protect against "typeless damage" from magical attacks.
However, if a magical attack specifically mentions that it deals bludgeoning, piercing, or slashing damage, DR affects that damage normally, as if it were from a physical weapon. (Otherwise the magical attack might as well not have a damage type, as it would only interface with B/P/S damage in a very few corner cases, such as whether or not an ooze splits from that attack.)
For example, the ice storm spell deals 3d6 points of bludgeoning damage and 2d6 points of cold damage. If you cast ice storm at a group of zombies, the zombie's DR 5/slashing protects them against 5 points of the spell's bludgeoning damage. Their DR doesn't help them against the spell's cold damage because DR doesn't apply to energy attacks.

—Pathfinder Design Team, 03/06/13

From the FAQ.