How does "-age" come from L "-aticum", with a change from "t" to "g"?

Question

-age (wiktionary)

From Old French -age, from Latin -aticum.

Cognates include Spanish -aje and Italian -aggio.

-age (etymonline)

word-forming element in nouns of act, process, function, condition, from Old French and French -age, from L.L. -aticum "belonging to, related to," originally neuter adjectival suffix, from L. -atus, pp. suffix of verbs of the first conjugation.

1.The sound change from "t" to "g" is too obscure to me, and how to explain this phenomenon reasonablly?

2.Is there any other word undergone the same change?

Answer 1

To get the ball started, here's an educated guess:

-aticum [atiku] > *[atsiku] > *[atsku] > *[atʃo] > [aʒə] (older French) > -age [idʒ] (English)

because [ti] is often unstable. The final -m was lost very early IIRC.

Answer 2

I was also looking for the answer of this question and had trouble finding a good, detailed explanation. Fortunately I found a book that might help anyone who would like to know how 'aticu, aticum' became '-age'. "Cultural and Linguistic Factors in Word Formation: An Integrated Approach to the Development of the Suffix -age", by Suzanne Fleischman (University of California Publications)