Museum conservators use high quality non-yellowing hxtal. They clean the parts scrupulously , measure the proportions exactly and mix on a clean glass plate with a glass rod. After adjusting the epoxied piece to stop any potential creep you need to let it sit for a week undisturbed to reach full strength. Fresh normally available epoxies can work well with the same precautions but it is not simple to get the proper mix ratio. Some will brush on a bit of the hardener to the joint later to assure enough hardener was applied.