Toner is a very porous material. If left alone and the board was etched' date=' you'd wind up with pitted surfaces or even hairline breaks from cracks that were too small to see with the naked eye.[/quote']
No, not in my experience. I've made plenty of board using magazine paper and I've met people who've had good success with plain printer paper. I'm not doubting that it may increase the reliability of the process but there are more cost effective and reliable solutions available such as the photo process.
Who cares? It's a silk screen which is just there to act as a guide for placing the components. Fair enough, white might look better but I don't think it justifies the extra cost and I've seen commercial PCBs with a black silk screen before. The only problem I've found is that the toner can be easily scratched off but that can be solved by covering it with a thin layer of conformal coating which is far more cost effective.
Attached are some pictures of a board I made using toner transfer. It's the first time I bothered with a silk screen and whist, it's not perfect, it's more than good enough to serve its purpose.View attachment 41312
View attachment 41313