I really like the pictures; they are quite good, especially for things that are not commonly seen. A few comments. Lead is from Old English lead (with long e) akin to Old Frisian lad (c long a), OHG lot, New High German Lot 'solder'; these nouns are all as far as anyone can tell and point to Proto-Germanic *laudan 'low melting metal'. This term is related to Proto-Celtic *loudon 'low melting metal' which is assumed on the basis of Middle Irish luaide which supports a derivative *loud-ia of the assumed *loud-on. The Celtic for 'red' is *roudo- (Old Irish ruad; related ot OE read OHG rot ... and is completely unrelated to these words for 'solder' though the words rime. I would guess your source, whatever it is made a wild (and wrong) guess about that and sought an explanation based on minim the red lead oxide used as a pigment, but the forms are accounted for in a very different manner by etymologists. Because p is lost in Celtic (pater > OIr. athair; the Uer- of Vercingetorix is uper- [Gk. hyper- 'super']) it is reasonable to imagine that PCt. *loudon is from earlier **ploudon; this could be Proto-Indo-European *plou-dhom ie the root plou- 'flow' meaning the 'flowing, ie low melting metal'; the same reconstruction would give Latin *plubum; a common and simple change of *oudh to *ondh would result in plumbum 'solder, lead'; thus the Latin and Celtic are probably reflexes of the same original form meaning something like 'flowing metal'. The Celtic possession of the Erzgebirge 'the Ore Mountains in SE Germany/Czech would account for the Celtic term's being loaned into Germanic.
Lat. aurum simply means 'gold' and is akin to Sabine ausom recorded by early Roman authors. There is speculation that the root *aus- is akin to that in *aus-os 'dawn' which similarly becomes Lat. aurora, but that is not known becaude the words are so isolated. Old Lithuanian ausas appears to be the same, but the accent of that word suggests a mising consonant after the u, something like *auXs-; in the case of aurora, a relationship to Skt. ushas is clear and the PIE mus have been *Aus-os- (where A is not the vowel a but a consonant the becomes a under very complex conditions -- this is Saussure's Laryngeal Theory and the X would also be a laryngeal). If that guess is right, then the relation to 'dawn' would vanish, but the relationship to Tocharian A wa"s, TB yasa would be clearer supposing *AuEeso-, and thus pointing to 'Au' as one of three original PIE metals.