Philip Newton's journal

My idea was for symmetry in the various affricate pairs: German has /pf/ and /ts/ and (at least in southern parts) /kx/, so it seemed natural to me to use πφ τθ κχ, respectively, for those.

From that followed the idea to use the θ~σ distinction to approximate ß~s, with θ always being [s] and σ being [s] or [z] depending on the position. So you would have Βυθεν "penitences (dat.)" and Βυσεν "bosom" (and Βυσσεν "busses (dat.)").

There may or may not be a correlation between θ = German historic z and σ = German historic s; I don't know enough about OHG/MHG to say.

I'm not yet particularly consistent about the orthography, though - especially the use of single vs. double consonants to denote long vs. short vowel sounds. I keep forgetting especially with χ, which "should" be double after a short vowel in words such as ιχχ but where I tend to forget since German only has "single" ch - since there's no double version of that in German, so "Lache" is ambiguous between "type of laughter" and "puddle". On the other hand, I decided σκ would also be ambiguous the way sch is in German, since it's a digraph.