They were undoubtably a strange couple - two artists whose character's were sufficiently peculiar that they could stand each other for relatively long periods. Michelangelo was particularly rude and impatient but found a connection to Sebastiano which lasted for many years. A full list of Michelangelo quotes can be found here.
Sebastiano must have had a strong self-belief in order to relocate from Venice to Rome in order to continue his development. He was in a strong position in his home state already and could have settled for continuing along that route.
Sebastiano was also one of the few people willing to stand up to Michelangelo, regularly suggesting amendments to their work. His tutor sometimes considered him a little above his station, but for some reason tolerated these outbursts.
Sadly their relationship would not stand the test of time as these two strong personalities would eventually clash to the point where they were not willing to work together ever again. One contributing factor would have been Sebastiano's humiliation in the Vatican delivered by Michelangelo's sharp tongue and cutting sarcasm.
Most of the evidence around their relationship was provided by regular correspondence through handwritten letters. Their later letters reveal the strain of the relationship during a turbulent time in the papal states' history, most of which involved political fighting.
Famous Quotes by Sebastiano del Piombo
When he speaks of you he seems to discuss one of his brothers, almost with tears in his eyes... he knows you and loves you... you frighten everyone, including popes.
Sebastiano discussing Leo X's opinion of Michelangelo
It is quite possible that Michelangelo used his colleague as a means to communication with others, with himself having a tendancy to alienate donors.
You do not seem terrible to me except in art, that is, the greatest master who ever was.
Sebastiano in defence of Michelangelo
Quotes by Art Historians and Artists about Sebastiano del Piombo
The Italian Renaissance is amongst the most studied artistic periods and whilst Sebastiano del Piombo is not the most famous contributor to this movement, his role was certainly considered significant. With this in mind, it is far easier to gauge opinions of his work than to find attributed quotes from his own lips.
The close relationship between Michelangelo and Sebastiano has ensured that most quotes from that period about del Piombo were from his master's lips. Aside from that, there is much to learn from how art historians have summarised his career.
... Oils are only suitable for women and idle people such as Sebastiano...
Michelangelo, aiming a parting shot at Sebastiano after their planning of the Last Judgement in the Sistine Chapel