Was it widespread practice to grant freedom to slaves in early Roman Empire?

Question

If a citizen owned a slave, he or she could free him / her. The Wikipedia article gives some reasons for doing this:

Slaves were freed for a variety of reasons; for a particularly good deed toward the slave's owner, or out of friendship or respect. Sometimes, a slave who had enough money could buy his freedom and the freedom of a fellow slave, frequently a spouse. However, few slaves had enough money to do so, and many slaves were not allowed to hold money. Slaves were also freed through testamentary manumission, by a provision in an owner's will at his death. Augustus restricted such manumissions to at most a hundred slaves, and fewer in a small household.

The later paragraph suggests it was later very common practice:

Already educated or experienced slaves were freed the most often. Eventually the practice became so common that Augustus decreed that no Roman slave could be freed before age 30.

It seems that "Augustus" means Octavian August and it would mean that this was quite widespread before Christianity, if it became a danger to state economy.

Do we have some sources confirming it was a widespread practice? How many slaves yearly were freed? (the text from Wikipedia does not cite any sources)

PS. I understand that there were many types of work, and they who worked in mines, galleys etc. were freed less frequently than those who were writers, baby-sitters etc.

Answer 1

There is a text of Cicero in which he defends a friend of his, named Milo. Milo was on trial for the murder of P. Clodius Pulcher, but manumitted (freed) all his slaves in advance. Roman slaves where required to be tortured for evidence against their master, hence freeing them will make this impossible. (Cicero, Speech in Defense of Milo 57, 58). I don't know to what extent Romans on trial freed their slave, but we can assume it happened more often, because the prosecutors of Milo suspected him of freeing his slaves in order that they might not be tortured.

When rich Roman landowners contracted a captain to transport commodities for them (like products from their estates) they often send an overseer with the ship(s) to look after their interests. This would often be a freed slave who had worked for them for many years so they can trust them, obviously the slave had to be a schooled one to administer his masters money.

I also heard in secondary school (12-18) of schooled slaves being allowed to work for themselves a part of their time, and keep some of the money for themselves so they could buy themselves free eventually.

Obviously these three examples are all house-slaves, and we might assume a certain affinity with their masters. I don't think slaves working on farming estates or in mines had the same chances of being freed, if any at all.

I don't think you'll find any sources on the amount of slaves that where freed, but i hope this helps.