charge on colloidal particles

jd12345

IS there charge on all colloidal partciles? My book states that charge is the reason why colloidal partciles are stable, otherwise they would coagulate
I always thought that it was their size that made them float.
I dont understand how they attain charge - they are not like ionic compounds such that they would get charge
For example :- metals sols like gold sols are negatively charged , blood is positvely charged
I dont get it. Where does this charge come from??
IS it necessary for colloids to have charge?

chemisttree

Review Zeta potential.