Lucid, pharmacology is a complex constantly developing field of science. You are at least right on one thing: this isn't the last time we'll be having this discussion. For now we can only follow what we know at the present and use that to get the bigger picture until something else comes around and completely changes the way we see the picture.
Blue, the pins and needles feeling you describe is known as vasoconstriction. This is normal with LSD and just can't be said to be a result of impurity, but rather physiology. Levels of vasoconstriction vary with dosage and one's physical factors at the time of dosing. For example if you are out in the bitter cold snow, you are going to probably have considerably more pins-and-needles feeling while on LSD than sitting in your warm-and-comfy living room. For myself I notice vasoconstriction more heavily on lower doses. This I attribute to the fact that I'm not "out of this world" enough to be able to ignore my physical effects. If it's dirty LSD I'm consuming then for some reason it's only dirty in small doses.
Red22, What you are neglecting to realize is that other impurities of LSD besides its stereoisomer iso-LSD have never been both detected
and quantified after synthesis to the best of my knowledge. That is to say they are practically undetectable, unidentifiable and not really worth mentioning other than for dispute. Factors such as epimerization, inversion, and polymerism do not allow for the generation of a significant amount of byproducts besides LSD's isomers. The reason for this as was mentioned by yours truly a few pages back is because of the carbon atom at the 8-position and its double bond linking it to the 5-position, rendering a very touchy molecule.
In the same post you will see I mentioned that the crystal of LSD forms its lattice structure with a great deal of difficulty. For that reason the appearance will be different each batch no matter the purity. You can't look at LSD and say it's purity/worth is this-or-that. I am afraid to say with a great deal of accuracy that ChinaCat72 (IF that is his real name

) is a misinformed former drug dealer unaware of LSD's actual science. To spread such as fact is a blasphemy to the force of science. Without quantitative analysis you cannot determine purity. You can't even come close.