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Maple splotching

D

Dan Stromberg

Joined
May 25, 2010
Messages
124
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81
Location
Prince Frederick, MD
Hi all,

I know that maple is very prone to splotching, but I'm wondering if that's really what this is. I finally finish-turned a rough ambrosia maple bowl I had on the shelf for a while. The dark spots appeared as soon as I applied finish (danish oil (TNT)). I also can't help but notice that they are also primarily around the end grain.

Did I do something "wrong", or is this just the chance you take with some woods? Wondering if there's something I could have done differently to prevent this. Everything was sanded to 600 grit before I had added the finish. Mold? Nothing I could see beforehand, but not impossible. If this were flatwork, I would have sanded the endgrain a little higher to compensate, but that's a little harder to do here.

Thanks as always for any input!

Dan
20201229_145245_50pct.jpg 20201229_145310_50pct.jpg
 
Thanks for the responses. I thought I did a light coat, but when it sucks it all in right away there's not much I can do to pull it out. :) On other woods, I've liked the way that danish oil has turned out. I've been doing multiple coats, separated by 24 hours at a time. The blotching happened almost immediately.

I don't mean for this to turn into another "what is your favorite finish" thread, but what would you have used instead that wouldn't have done the same thing? I would guess that most of the penetrating oils would do the same thing...

Dan
 
A wash coat or 2 of 1# cut of shellac should still allow the oil to soak in. I've had good luck with that. I wouldn't try it on my main peice, it's the kind of thing that needs some experimentation.
 
Glenn Lefley said:
Sanding sealer does what it is suppose to do, seal the wood. All finishes after that will be just on top of the sealer, ie lacquer etc. Oil would not work as it needs to soak into the wood!
Click to expand...

I am by no means a finishing expert (obviously, or I wouldn't have started this thread!), but my understanding is that the first coat of essentially any finish functions as a sanding sealer - after that the wood is sealed and you are just adding coats on top of the previous ones. I'd have to dig up the quote from my Flexner book to be sure, but that was one of my take-aways from the book.
 
Dan, the end grain will probably always look darker, but another consideration is whether or not the end grain was sanded as thoroughly as the side grain. I know you sanded to a fine grit, but perhaps there was not enough sanding with the initial coarse grits, or you didn't start low enough. Finer grits will still take the "peaks" off, and the surface will feel smoother. But the "valleys" can still remain. Just a possibility for your consideration.
 
Yes it is blotching and caused by end grain, whether you sanded great or not. That, and the color of whatever finish is used. Even blonde shellac will cause it, just less noticeable due to the light color and short open time. With flatwork I use a conditioner, either glue sizing or a wb finish thinned ~ 1:1 with water. The best conditioners are wb, and for them to work best the wood needs to be pretty saturated, which causes turned pieces to do funny things like warp or even crack. You can try multiple lighter coats of conditioning to if that helps, but it starts to defeat the purpose of a conditioner - get more into the areas that need it.

With turned pieces I just let it go, as to my eye it adds to the character of the piece. The more color the oil or varnish has the more blotching is noticeable.There are water clear wb finishes available but they have no chatoyance. Most solvent lacquers will yellow with time. Find the clearest oil or varnish to reduce it if you want the chatoyance and the simple application method.
 
If you experienced any end grain tare out in the turning process it can take a lot of sanding with 80-100 grit to get through it. I have found that a scraper used flat on the tool rest prior to sanding Soft Maple will just just make the tear out less visible. I then tend to start sanding with a higher grit and not remove all the tear out.
 
One of the reasons I always do a wipe down with mineral spirits (other use other things) after I'm done with 240 and even again if I'm not sure. It's not uncommon that I think I've sanded well and it will look fine and then I wipe down and there it is, a tool mark, compression mark, sanding ridge or blotchy look in some places. Typically end grain areas. I go back and keep at them until I get the wipe down to look like I want. I use walnut oil so less prone to the blotchy looks but it can still happen if I don't check first.
 
Thanks, guys, for all the great input - as I knew there would be. I did wipe the piece down with DNA before finishing, but to be honest I was paying more attention to getting rid of the fine dust than I was about looking at the surface before it evaporated.

Mark, I liked your description of the "peaks and valleys". It made for a perfect visual.

Well, this piece, like every piece, is a learning opportunity! By that measure, I'd say it was a success. :)
 
At first, I thought it was probably tear out. If it was tear out, then the dark coloring would be spread through the end grain, and not in streaks like the pictures show. Generally, tear out is on the 'uphill' side of the cut, and those stains are on either side. I would guess that the coloring was in the wood to begin with, and the finish high lighted it.

robo hippy
 
Robo makes an excellent point. Many times I see a finish darken and make grain figure more prominent. 2 types of products you could try for alleviating the darkening - gel poly, or a thick oil like blo out of the can or one of the low voc pre- polymerized linseed oil “hard wax oil” type products. The higher the viscosity the slower the penetration. All of these products have an bit yellow to orangish tint but possibly less than natural do, but the much higher viscosity will limit penetration.
 
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