Can someone please explain what Tamil aytham originally represented
and now represents in Tamil? I'm particularly trying to find out if
it has any real connection with say the Hindi /t/ ~ /tH/ ~ /d/ ~ /dH/
distinction. One scheme for representing the contrast, at least in
writing, in Tamil, is to use superscript/subscript numbers, and that
scheme I understand.

One Sinnathurai Srivas, who frequents the Unicode mailing list ( ) and its Indic script list (archived
at if you're interested in
reading raw e-mails - same publicised username/password for access -
unicode-ml/unicode) has recommended that I read his articles at:

Unfortunately, they correspond ill with what I can find out from other
sources, so I don't know what to make of them. As far as I can see,
the primary modern use of aytham is to represent foreign
_fricatives_, and that is neither complex nor relevant to the
representation of Indic sounds in the Tamil script.

Sinnathurai Srivas does come across as an eccentric Tamil chauvinist,
but he sometimes has some valid points, so I can't just dismiss him
out of hand. It doesn't help matters that he seems to have a Tamil
spelling reform agenda of his own.

I am aware that Tamil contrasts voiceless and voiced stops, though
some Tamils vehemently deny it. I have seen independent statements
that aytham was connected with glottalisation in Old Tamil, but I
can't see how to connect that with anything in Modern Tamil. I'm not
even aware of any comparative Dravidian relevance.