CAMBRIDGE, MA — London’s The Foundry, makers of Nuke, Furnace and Ocula, has sold off its Tinder and Tinderbox visual effects plug-ins business to Cambridge-based GenArts, which offers Sapphire, Monsters, Raptors and most recently ParticleIllusion. GenArts will begin development, sales and support immediately. No staff will change hands, but engineers at The Foundry will continue to work closely with GenArts going forward.