Actually a pre-etch is not required if the gloss is first removed from the copper. 000 steel wool or 1000 grit wet and dry followed by a cleaning with water or IPA works fine too.
Of course contamination with skin oils from handling is to be avoided.
I'm afraid you and I are not on the same wavelength. This is why so many people are better off with UV. In the surface, toner transfer is simple. But there are some minor nuances to get consistent and accurate results. And the signal to noise ratio on the subject is very very low and expectations and techniques and results vary quite a bit. A lot of the information is old. And there are a lot of recent videos and webpages about it. Mostly with old information. Even 20 years ago, people were saying that a pre-etch is useful. And other people were saying that it is optional or not necessary.
IMO, pre-etch is essential if you want to completely liquify the toner. Cleaning the board is essential, period. And I use steel wool for that. The toner will have no trouble sticking to the copper if you just clean with steel wool or sandpaper.
The pre etch makes the surface porous, so that it sucks up the liquid toner instead of squishing it around. After cleaning the board, I dunk it in the etch tank for a few seconds and then rinse it off in a bucket of water. That's all a pre-etch is.
The predominant school of thought is to just barely/partially melt the toner. This is a very fine window with failure modes if too cold or too hot. If you pre etch, you can crank up the heat until the board bubbles and delaminates, and the transfer will still be fine.
This wasn't practical even 10 years ago.* The melted toner would suck into the paper and leave a mess of fibers on the board. Or the PnP would melt and distort. Today, this is the way to go, using Pulsar dextrin coated paper. Welcome to the 21st century.
I'm not saying I can make better boards than people who do not pre-etch or do not use Pulsar. I'm claiming that I can make a board once a year, any size, thickness, mass, down to 8 mil traces, and it will come out perfect on the first try, every time. No particular attention to detail or timing or muscle memory needed. It is foolproof. Just do the steps.
*unless you are one of those guys that stumbled upon the mythical legendary Photo Paper. The one that they changed the fomula of and/or discontinued by the time you posted about how great it is.
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