You can use the PCB with bear copper tracks but they will quickly start to oxidise. I applied a coating of liquid Tin. Just immerse the board in the solution for 1 to 4 min depending on the thickness of the coating you require, I left it in for 2 min. Its best done straight after you have removed the etching mask with acetone and the newly exposed copper is not contaminated in any way. With all these processes you need to regularly if not constantly agitate the solution to aid its progress and prevent small air bubbles from masking areas. The Tin coating is only a few microns thick but it protects the copper and makes soldering easier. As you can see, the level of detail achievable with this process is very fine, as a guide, the hole guides for the component legs are 0.5mm dia on the artwork and the lines around the edge of the board (cutting guide) are only 0.2mm wide.