RobF -> RE: dark shellac performance (Jan. 21 2019 17:57:53)
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so, rob, now it would be time, to try your suggestion. how do you do that alcohol wipe of-thing? This response might be way more detailed than you wanted or need, but here goes... What I do is pour about a quarter of a cup of 99% alcohol into a bowl, put a nitrile glove on my working hand, dip a cotton rag in the bowl of alcohol and get it good and wet. I then wring it out a bit and protect the guitar from drips by holding some newsprint under the rag as I move it from the bowl to the area of the guitar that I want to address. I place the rag on the area I want to strip, get it wet, and let the alcohol sit on the spot for about a half a minute. It’s important to not let the area get so wet that the alcohol runs but, to be safe, I have another drier rag on hand to wipe any runs before they can get too far. The alcohol will start to dissolve the shellac and it can be wiped off. It generally takes a number of gentle wipes and often a re-soaking of the rag to get it all. I just keep dipping the rag in the alcohol, wring it out, then bring it back to the guitar. Don’t worry about the alcohol damaging the wood, it won’t. Until the shellac is gone, it’s working on the shellac, not the wood. Once you’re down to wood it essentially has the same effect as the spit coat done when prepping the top prior to polish. It’s not a bad idea to not let the glue line joining the panel get too wet, however. Just to be safe, I work fast in that area, especially when it gets close to the wood, I don’t like leaving it wet for very long. I tend to work on spots of about 9 square inches at a time (about the size of the soundhole). It’s good to start in the middle of the panel and work your way to the edges. This will give you a chance to get a feel for how the shellac will respond and will help you determine how much alcohol the rag needs to be effective. We want to avoid having things so wet that the alcohol runs over edges to places where it doesn’t belong. It’s also important to pay attention to the areas beside the fingerboard, over the rosette, and along the binding. There is a tendency to leave traces of old shellac in these spots and that should be avoided. You want to clean everything off. Otherwise it will show when you do the re-polish. For the edges along the binding I keep the rag fairly dry and rely more on vigorous light rubbing to remove the shellac than using lots of alcohol (again, to avoid runs). When working along the fingerboard, watch the pressure and be careful not to use a fingernail to try to push the rag closer into the corner. The danger in doing that is the nail could potentially put grooves into the wood of the top. Just an interesting aside.... I often mix different resins in with my shellac, gum benzoin being one of them. It smells nice and has the characteristic of imparting a high shine. For my last guitar I didn’t use it in the preparation and I found the shellac seemed to build up easier (and faster) than with mixtures containing benzoin. As luck would have it, I did have to strip the top on that guitar, just a couple of weeks ago. Now this is based on a data set of only one guitar, but I found the non-benzoin shellac stripped off much easier than a shellac prepared with benzoin. With some of the guitars I’ve stripped that were polished using a preparation containing benzoin I really had to work to dissolve the finish. They were close to impervious to alcohol spills if the spill was wiped off immediately. I haven’t done any heavy duty experimentation with this, it’s just an observation I made on one guitar, so take it with a grain of salt. But I’m thinking I might try reserving a preparation containing benzoin for the final couple of sessions, and do the bodying with a preparation that is without it. Anyways, I think you’re making the right decision to redo, best of luck. It’s a good learning opportunity. That thread Jason linked to is well worth a read, too.
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