Unless I remember wrongly, there's a difference between primals and eikons, and it's not just a mistake in etymology by the Garleans.

The Allagans used "eikon" to refer to a particular class of entities -- the Warring Triad, for example -- but, admittedly, it's still not clear exactly how eikons differ from primals.

It seemed, though, that with regard to the Warring Triad, all three eikons were capable of inadvertently tempering individuals who came too close to them.

Frustratingly, Odin/Zantetsuken is also an eikon, by Allagan reckoning, but its tempering effect appears to be more deliberate.

So, in short, there are different varieties of tempering, and it does appear to be deliberate in many cases. The Scions who encountered Ramuh, for example, were not affected, because the primal chose not to temper them.