I've been heavilly sanding away at my Douglas Fir floors for some time with my u-sand machine. Most of it is the original narrow boards from when built in 1911 and some is newer 3.5" from when they extended the living room into the porch. Okay I've read that it's a wood that does take on a red tint over years which I can see but it still comes up well but there are some areas which have these deeper red/purple marks (like when you see some one with a strawberry birth mark). I've sanded and sanded but it really seems to be deep in the wood.

Last night I decided to apply my sealer in a corner to see what it came up like. I'm using Interlux 1026 clear which is a boating product, we sell it at work and guys have recommended it, I have no issue with this, it's a nice amber natural color on the good part. But...the purple marks have just gone really dark and I don't think I can look at them and think "yeah nice antique look".

So my I'm looking for suggestions, I'd like to keep the wood a light color but have this feeling I'm going to have to stain it dark to make a more uniform look to the job. I've used wood bleach and hrdogen peroxide, both of which helped a little. Thanks!

Photo showing my test sealed area
http://www.flickr.com/photos/7245590@N05/2550529989/

Another photo showing blemishes
http://www.flickr.com/photos/7245590@N05/2405819764/sizes/m/

This is sealer I'm using.
https://secure.international-coatings.com/pds/yacht/GB_ISO_I_5000179.htm

This is very common with old doug fir and there is really no good remedy. You could sand forever and not get rid of this "bruising" of the wood. Nor will bleaching get rid of it completely. Plus, repeated bleaching breaks down the cells of the wood making a soft wood even softer. This is why many older fir floors were painted. To completely hid those darker sections, you would need to stain very dark or paint. My motto in refinishing is work with what you got and do not try to make it something it isn't. There is an historic house near my home that has fir everywhere. But to make that cheap wood (at the time) look expensive, they "grained" it using faux painting techniques to make it look like flame maple. A clever approach that was commonly done in the late 19th century. But to your situation. If you want the floors light in color and without those darker blemishes, you will need to paint. You could consider a light color well thinned out. Then poly over that. Or go with a very dark stain that will hide the bruising somewhat. Some paint these floors and then stencils patterns on then. And after that, apply a couple of coats of waterbased poly over that to ensure longevity. Good luck with whatever you decide.

Gary, thanks for the informative answer, I guess you've pretty much confirmed what i was thinking (sadly). I think staining is going to be the way forward as i really don't like the idea of painting.

One question is that i sanded using 120 to before using the sealer as that was what they recommended but I have read on here that people usually only say to use 80 for staining/sealing to let wood soak up better, might this help a little? (I can't imagine fir not soaking up anything though..I could try it myself on another patch)

Funnily enough i did come across the following photos which show new fir floors with quite a marbling of tones so maybe I don't have to go too crazy with dark stain. Just keep building it up until I feel it's livable.

http://www.douglasfirfloors.com/photos/glue_down_floors.htm

Here are a couple of fir floors that I have done.

The darker one with the bad paint is a water popped red mohogany. With Bona Mega applied.

The hall is a custom Drifast stain and Traffic. No water pop.

I recommend the water popping for fir.

http://gallery.mac.com/barquios#100008

Thanks for the photos. I sealed the whole room and it's pretty clear I'm going to have to stain and go pretty dark, shame because I really like the color it has come up on the non bruised parts plus it's gives so many more options on what colors to use for the rest of the decor.