A man, who for a long time has been suffering from chronic mandibular osteomyelitis, died of renal failure. Autopsy shows enlarged yellow - white kidneys that are extremely dense and have a waxy sheen. Light microscopy detected deposits of homogeneous pink masses in the glomerular capillary loops, walls of arterioles and arteries, canalicular basement membrane, and stroma. These deposits color black - red, when stained with Congo red. What process developed in the kidneys?