I have suggestions for two new elements.  They're 2 of the 4 electrical phenomena that exist in real life.

1. STFE--Saint elmo's fire (not the movie)

STFE looks and is shaped like LIGH, but glows an eerie blue when fire display is on.  If a conductor (except TESC and ETRD) or semiconductor (except SWCH, INST, WIFI, and WWLD) was sparked by LIGH or THDR, the SPRK will emit STFE as it travels along the conductor or semiconductor.  Like EMBR, STFE exists primarily for graphical effect so it's only fair that it's placed in the "hidden elements" category.  But also like EMBR, it can be useful.  Besides creating dazzling light shows, STFE is also ideal for use in realistic Jacob's ladders--which would otherwise be difficult to make in tpt.  STFE will spark conductive materials only when it's spawned by brush--not by SPRK.

2. BLIG--Ball lightning

BLIG looks like THDR, but glows cyan when fire display is on and is a solid.  Like SPNG, it can move when it has set velocity and, like LIGH, it can phase through walls.  It's spawn temperature is 9000C, if spawned by brush.  Like LIGH and THDR it sparks conductive materials upon contact.  It's intangible to all elements, like sparked e-wall, but will burn flammable elements (even virus) and explode explosive ones (except C-5.)  Can be made when STFE is mixed with PLSM.  Useful for making stars without the need for newtonian gravity and can also be used as a largely indestructible battery--more so than CONV(SPRK) as BLIG is immune to virus.  It should be in the "explosives" category.

I have an idea that will remedy that:  add pavg to SPRK.  SPRK's pavg0 will match the ID of the element that created it (for example; if it was spawned by BTRY, pavg0 would be 53.)  A brush-spawned SPRK would have a pavg0 of none.  SPRK'S pavg1, by default, matches the ID of the element that matches it's ctype.  But if you change it, then the SPRK will change the conductive material into another element as it travels along the conductive material.  In this case, SPRK with a pavg0 of 48 or 87 will emit STFE as it travels along the conductive material.