A couple of Marconi Rosso sweet peppers finally sprouted with my Big Jim sweet peppers on rock wool cubes. On my first failed attempt with rock wool, I stuck the Marconi pepper seeds tight into the rock wool cubes with a tweezer and had them under a small grow light and heat pad.
On my second attempt with rock wool, I placed the pepper seeds loosely in the premade hole and kept them covered with a black t-shirt with no heat mat and after a few weeks I saw a white root pop out from one of the seeds and moved the seed tray onto a heat mat under a small grow light and now I see green foliage and other seeds sprouting.
I think covering them at room temperature for a few weeks and then moving them to the heat mat under a grow light made a big difference. However, it could also be the way I placed them loosely in the rock wool hole and kept 1/4 inch of the rock wool cubes submerged in water.
I will take out the first sprouted seedling tomorrow, so I can keep the seed tray covered.