It's like taking a picture with a film camera. In both cases, the exposure to light causes a latent change in the photosensitive material. You have to use a chemical developer to process the latent change into a usable change. Jason ----- Original Message ----- From: "Hopkins" To: Sent: Monday, June 21, 2004 10:33 PM Subject: [EE:]PCB Making I have purchased RS Components Aerosol photo resist 198-9651. They suggest that I need to use a there "Universal Developer" 690-849. Is this really needed as it is expensive. I thought the UV light exposure would soften the photo resist enough for etching - but if this is not the case then what does exposing to UV do? I was just going to use the photo resist then etch it. ************************************************* Roy Hopkins :-) Tauranga New Zealand ************************************************* --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.708 / Virus Database: 464 - Release Date: 18/06/2004 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.