(EDIT, 4/23/16: Up to date information about the Intranquil Sprit can be found in my new book The Intranquil Spirit, available on Amazon. This post is mostly correct, but has some incomplete information.)
I've done many an Intranquility Spell in my lifetime -- being that I'm a professional magic spell caster that is, of course, logical. However, there seem to be many misunderstandings about this important type of magic spell, which are circulating the internet and invading the minds of people who might (or might not) benefit from its use.
#1. The Intranquility Spell is evil.
The Intranquility Spell is no more evil than trying to get the same results by way of any other spell. Now, one might argue that the intent is evil, or at least selfish -- but I have had people who requested the exact effects which an Intranquility is meant to bring (desperation, obsession, pining away) yet who refused to do an Intranquility spell specifically on the belief that it's the spell and not the intention that is evil. That's rather like saying a knife is evil because you can murder someone with it, but that a gun is okay to use to murder someone because it's not a knife. The intention, not the spell, is what dictates the goodness or badness of a working.
#2. The spell backfires so that the Intranquil Spirit haunts you instead.
I used to buy into this idea, but over time, I have come to conclude that the people who make this complaint are people who were either plenty obsessed and distraught to begin with, or else who were already inclining down that path before they cast the spell. (Indeed, it's an unhappy, obsessed person who usually wants to make their would-be lover equally unhappy and obsessed.) It does make one think that Intranquil Spirit spells ought to have a warning to only be used by people in healthy mental states, lest it makes trouble for a person imagining themselves cursed or haunted by it when their problem actually is rooted elsewhere.
#3. The Intranquility Spell must be done with a specially crafted, glass-encased, pink wax Intranquility Candle.
The Intranquility spell can be cast using any kind of candle. Even the standard "Intranquility Candle" is not actually an Intranquil Spirit candle -- it's a design called The Omnipresence of God. It is a basic Catholic religious candle whose design is being completely repurposed (possibly because of the eyes, ears and hands in the design relating to the prayer's request to command the spirit to overtake the victim's five senses, as well as the skull image near the bottom relating to the dead.) Some people also use Anima Sola candles in lieu of Intranquil Spirit/Omnipresence lights. In short, the Intanquil Spirit has no official imagery and all candles for her are repurposings of other things.
I have trouble finding the pink Intranquility candles in my area, and so I often cast the spells using plain red glass-encased candles, or sometimes pink free-standing candles. I've also used plain white emergency candles for it, in urgent cases. All the spell really is, is a prayer to a spirit for help. I would personally say that it's only important to use a branded Intranquil Spirit candle if you don't intend to use any dressing oils -- but once you've dressed a floral votive candle with Intranquility oil and said the prayer over it, the votive is just as good as the big glass thing.