Just curious...
The Investigator archetype Antiquarian RAW does not suffer arcane spell failure.
A Wizard dipping into, or a start-as Investigator Antiquarian then Wizard forevermore allows for an armored wizard with no spell failure chance.
Typically the archetype or class will specify that it's only for their class's spells like, "A summoner can cast summoner spells while wearing light armor without incurring the normal arcane spell failure chance.",
but I suspect that the antiquarian's lack of specificity isn't meant to apply to other class's spells regardless.
I'm not certain though, the only archetype or class I can find that removes spell failure and doesn't specify that it only applies to its own spell list is the fighter archetype "Child of Acavna and Amaznen", and that does seem like it's intended to function with other class's spells.
The antiquarian's ability to ignore spell failure is part of their 'relic casting' ability which specifies how their own magic works. I'm pretty sure it's meant to work with antiquarian spells/not-quite-extracts.
There are plenty of places where the rules are redundant.
Hast specifies that you only get +20 feet of movement if your speed normally 20 feet. Expeditious Retreat has no such language, but you still follow the same rules as Haste, because those rules are in the encumberance rules.
They didn't actually need to put the extra text in Haste, they just added it because it's easier for players than having to look it up in the spell and in the encumberence rules.
Wizards still have arcane spell failure for casting wizard spells.
Believe me , I am very aware, "specific overrules general," but the wording of the archetype regarding the is very general, "does not suffer arcane spell failure." Does not say in regards to relic casting specifically.
I think this is a RAW vs RAI situation. Intended to be relic casting only, but not worded to be definitive in that regard. Just wondering if anyone tried it.
Sure, then generally they suffer no arcane spell failure, but specifically their wizard spells do.
Problem solved.
I actually think that RAW, it does work as the OP said, because of this FAQ saying "General rule: If a class ability modifies your spellcasting, it applies to your spells from all classes, not just spells from the class that grants the ability." I would say that the line "An antiquarian does not suffer from arcane spell failure." does indeed modify their spellcasting, thus the FAQ is to be applied.
I'm sure that's not intended. The archetype is from a soft-cover splatbook, written by a freelance writer, and produced at a time this book when by self-admittance Paizo had stopped content editing PF1 books to focus on PF2 instead.
Note that there is no mention in the Antiquarian archetype of changing the spell list, so this archetype basically gets to cast alchemist spells/extracts as arcane spells on himself or others. That is not an overpowered advantage.
And I wouldn't be so quick to disparage the quality control of Player Companions a year before the end of PF1. The people working on those books then were mostly the same people who are working on the Lost Omens line now.
Cool, so he can make wands of "alchemical allocation"? I'd been looking for a class that could do that.
Of course, a Wizard losing a class level is a very high price just to get a few points of AC, so it's not really a balance issue.
Well... with the much talked about and generally agreed upon arcane caster vs. martial disparity... I'm thinking not so high a price to pay.
Dipping a single level to wantonly cast fireballs hither and yon while flying around clad in Celestial Plate Armor... Not a bad visual... And even MORE caster vs. martial disparity I would posit.