Wet Work - Washing, Deacidification & Bleaching
Matt said:Re: Wet Work. How long do you bathe the poster? Daybills being thinner than one sheets would have less time in the bath?
Charlie said:Great question. Not really, for say the initial soak and deacidification. I am at 20 to 30 minutes before my first rinse after the CaOH pretty much any poster. However, a byproduct of the CaOH turns the water yellow (maybe brown - I am color blind) and if that happens to a significant degree, I will do another 20 minute soak... Now for bleaching, it's all a big babysitting job, you never leave it. Unless, you want to be really conservative with a weak solution that takes a good hour to work... It's usually a 15 minute event, unless there are spots that need attention... There are actually two methods I use. Let me get to a desktop and I will discuss those.
Charlie said:Ok so the two methods.Method 1: Complete ImmersionThis is taking the poster(s) and placing it in a tray, or the like, with a solution that has been calibrated to a pH level 10-12. Leaving it for the prescribed time.Here is the "left-overs" from a set of daybills I did for you. I soaked them because they are smaller and the tray is manageable.Method 2: Spray On MethodThis is taking the poster against a mylar sheet and after it had been completely made wet and excess water mechanically removed - soaking the poster with by spraying a prepared solution (g/L) on both sides and sustaining the presence of that solution between two mylar sheets. This is actually easier and more difficult because you have to respray in 5-10 minute intervals to ensure that the poster remains completely wet with solution. If it does not remain completely wet discoloring may appear as the CaOH solution does act as a mild bleach as well... It's a constant babysitting job but one where you are only preparing a 1L solution versus a 10 liter bath that is then pitched.FYI here are some common deacidification methods that someone my find of interest: