Throat burning: Possible contamination or...?

[Lethargy]

Some time ago SWIM extracted some yellowish oily crystals from MHRB powder. As he had no prior experience he wonders if he did something wrong with the extraction or if instead the ingestion...

After heating the crystals and inhaling he got some minor effects (buzzing, entities peering at him through walls) but each time he inhaled he felt a harsh, burning feeling in his throat. Now SWIM has burned the hell out of his throat a few times smoking other things and this felt different somehow. He got it in his head that perhaps some of the base used in the extraction had gotten into the final product and so drank a vitamin c based fizzing drink and it seemed to help a bit more than water. For the record, SWIM couldn't swallow without irritation for about 3 days, so he'd consider the burning serious rather than mild.

SWIM has since dumped the product but wants to try again, but doesn't want to give himself a chemical burn OR just an ordinary heat-based burn.

SWIM used VM&P Naptha (which when evaporated in a glass baking dish left the slightest hint of residue, like fingerprint-oils) and lye crystals dissolved in distilled water.

Could the burning come from trace amounts of lye/water getting into the naptha layer or does SWIM just need to work on getting down the vaporization temperature?