-ind /aɪnd/ and -old /əʊld/ are diphthongs, -ond /ɒnd/ is a short vowel
9-10c: Homorganic lengthening. Because -nd, -ld, -mb, -rd, etc. articulate on the same place in the mouth, vowels before them became long
bind < binde (/bində/ ME) < bindan (/biːndan/ OE) < bindan (/bindan/ OE)
bond < bond (/bɔːnd/ OE) < bond (/bɒnd/ OE)
bold < bold (/bɔːld/ ME) < bald (/bɑːld/ OE) < bald (/bɑld/ OE)
child < child (/tʃiːld/ ME) < cild (/tʃiːld/ OE) < cild (/tʃild/ OE)
Exception: remained short if followed by another consonant
13-14c: Reversal of homorganic lengthening. Long /A, E, O/ tended, but not always, to be shortened
15-17c: Great vowel shift. Long vowels became diphthongs
bind < bind (/baɪnd/ EModE) < binde (/bində/ ME)
bold < bold (/bəʊld/ EModE) < bold (/bɔːld/ ME)
child < child (/tʃaɪld/ EModE) < child (/tʃiːld/ ME)
Special case: fond is derived from fonned (OE), not -nd, hence not homorganic
Special case: wind (NOUN air moving) pronounces /wind/, while wind (VERB to turn) pronounces /waɪnd/
16c: wind /waɪnd/ for both meanings
18c: assimilating to windmil or windy, which were shortened due to the "Exception" case above, wind became short /wind/
Evidence that wind (air moving) surely pronounced /waɪnd/. In Shakespeare's As You Like It お気に召すまま
Blow, blow, thou winter wind
Thou art not so unkind
As man's ingratitude
Thy tooth is not so keen
Because thou art not seen
Although thy breath be rude