I don´t know why but after some time, maybe a week or two, my projects start having some black spots. I have no clue where that comes from. I have been making toys from hardwoods and never had this problem. I thoughit may have something to do with too much sanding so the second (dark) layer, starts to apear through. If I remember well I treated these with safflower oil only and let dry in owen for about 20 minutes at 50°C. What do you use to treat plywood? Do you also use any sealer after oil dries? Would using oil mixed with beewas be enough?