iron stains in oak--paste wood filler

[Anne Schmidt]

Fellow Finishers,

I could use your expert diagnostic skills because I am refinishing an oak dining table top & leaves, but my experiments are not producing the results I imagined but black iron spots instead. I need help interpreting the results(or perhaps facing facts I wish were not so). Hoping someone has experience because I've already experimented for a couple of days now.

The experiments on the back of one leaf involve in order:
1. sanding,
2. vacuuming,
3. scrubbing out grain with Denatured alcohol and either brass or stainless wire brush(different test areas)
4. sealing with shellac/or not
5. water-based grain filler(famowood & dry pigments)applied with plastic scraper.

. . . and then appear black spots in some of grain, regardless of brass vs. stainless brush, regardless of sealing with shellac or not. But only certain areas of the oak . . . where it's pores are at 30 degrees approx. as opposed to flat sawn areas and resinous and dark-ish looking to begin with.

Is there a way to make this work?

Much appreciate any thoughts on this tricky situation.

Thanks, Anne Schmidt

[John TenEyck]

I haven't had this happen, so my comments are purely conjecture. I'm guessing there are iron particles in the wood, under the old finish you removed. When you applied the water based grain filler it reacted with the iron creating the black spots. I think this could happen whether or not you put on a seal coat of shellac, since one coat isn't going to completely seal the wood. Another possibility is that the iron particles are in your filler. In either case, switching to a solvent based filler would solve the problem. Hope this helps. Worth a test. Good luck. John

[Anne Schmidt]

Thanks for responding. "Pure conjecture" huh! I like that. It's a good term for what I've been doing a lot of lately.

Here's a pic of the issue.IMG_2655.jpg
Could be iron particles in the wood reacting with the paste I guess. Or, maybe it's some other equally nefarious chemistry . . . my husband dragged out his "Henley's Twentieth Century Book of Recipes, Formulas and Processes" which had a whole section on filler and mentions a common problem which occurs with oak involving albumin from the pores and tannins and caustic elements in the filler. How would I know?

I've heard really good things about oil based fillers but I prefer to use less toxic materials when possible. Not quite ready to give up on this yet. I'm going to try this method again except I will apply the sealing coat of shellac like I mean it next time. I'll thin it more and work it into the pores. Let it dry. And then do that again; see if that won't plug up those contaminated pores.

Failing that, I may try the shellac filler method described in the recent discussion in these pages. May take a bunch of coats but at least it's straight forward.

Will post results as soon as I get back to this--probably mid week.

Thanks Again, Anne Schmidt

[Chris Fournier]

I don't know enough about the specific "dry pigments" that you are using but the earth oxides that I use to tint filler etc contain iron oxide. Perhaps you should try your process and leave out the dry pigments. I realise that iron oxide is not the same as iron but perhaps there are traces of iron in the pigments? Because you specified that you used brass and stainless brushes I'll assume that no steeel wool was used on the oak.

[John TenEyck]

Good luck, Anne. For what it's worth, there's not much toxic about solvent based grain fillers. A little mineral spirits, or similar solvent, some oil, a little varnish binder, and the filler. And you can top coat it with most anything, including water based products, as long as you let it dry completely.

[Anne Schmidt]

I don't know enough about the specific "dry pigments" that you are using but the earth oxides that I use to tint filler etc contain iron oxide. Perhaps you should try your process and leave out the dry pigments. I realise that iron oxide is not the same as iron but perhaps there are traces of iron in the pigments? Because you specified that you used brass and stainless brushes I'll assume that no steeel wool was used on the oak.

Thanks for writing. Yes, there are iron oxides in at least some of the pigments I am using--amberg yellow, French ochre, & burnt sienna. Come to think of it though, I have used these pigments to tint fillers for other purposes with no ill effects, but never with oak. so maybe they are reacting with water especially under the influence of whatever's in those pores. Teasing out their effect with a test would be a good idea; wish I had some untinted famowood(no clue what colorants were already in the colors I started with).

But yeah, iron. Sure does look like iron stain. Right, I did not get anywhere near it with steel wool, but it is about a hundred years old so I have no idea how it was handled previously.

Here's another caveat: the underside I've been experimenting on has never had any finish except age and that makes for one situation; the top side may behave a bit differently. Can't wait to find out. : \

You will know as soon as I do. Thanks.

[Anne Schmidt]

Good luck, Anne. For what it's worth, there's not much toxic about solvent based grain fillers. A little mineral spirits, or similar solvent, some oil, a little varnish binder, and the filler. And you can top coat it with most anything, including water based products, as long as you let it dry completely.

Yeah, you're definitely tempting me. Too bad that it doesn't take "much" of anything toxic to give me a headache. (I even get a headache from denatured alcohol after a long session of french polishing .. . I guess it's the methyl ethyl ketone it contains).

. . . I often dream of just taking those heavier duty products for a test spin, but I might get hooked. . . and then where would I be? I'm like an alcoholic, I remember and love the stuff, but I'm just so sensitive; it's like one sniff might just take me to a gate I don't want to go through.

Like others, I have found over the years that most hard-core products do perform better--like plain ole enamel house paint. However, given that I plan to be doing this sort of work more regularly for the foreseeable future, I recently made a resolution to invest some energy in figuring out to make the most of the "less" and non-toxic materials. I want to bring the toxic bar down so I can get over it more easily every day and not need to hassle as much with a respirator. (besides can you imagine the wrinkles that constant use of a mask would cause . . . eeugh!)

If you can handle the stuff, more power to you. Just for today, I'm sticking with water ; ). --Thanks

P.s. But don't take the good stuff off the table. I might change my mind later.

[Peter Clark]

I'm responding from distant memory here but there is an acid solution that will remove the blue stain. Its the same acid in Lemon Juice. I have used Lemon juice before. I don't remember the "proper" name. I suppose without removing the mineral cause it would reappear after several years... Just a thought.....

[Anne Schmidt]

Yes. I read something about that too. . . someone mentioned it as a first line of offense used with salt as a bleaching agent. There are a bunch of articles around about various methods of beaching wood. personally,though, I've never seem blue stains on wood, only black or rust.

[Anne Schmidt]

Please stay tuned. I am now writing up the results of recent tests and will post as soon as they are presentable. Thanks.

[Anne Schmidt]

Before I give the results, a recap of the point of this exploration: I’m trying to develop a non- to less-toxic method of cleaning, filling, and finishing an early 20th century oak dining table, but ran into iron stain problems early on.

When I last left the forum, I resolved to do what I thought was a simple test. This test--whether or not more, but thinner coats of shellac sealer would prevent the iron in the water-based filler from reaching and reacting with the oak’s tannin-chocked grain and causing black stains--however, ended up bringing up more questions than it answered, so it took a while to get to the bottom of them. Hope no one was holding their breath; here’s a summary of my results:

I made 3 samples on the same board--1 vs 2 vs 3 coats of thinned shellac--but was so sure of the results, that I hardly looked at the samples until the whole finish process was done. Then I was shocked to find that the patch with the most shellac sealer also had the most black blossom stain. However, it was hard to be sure exactly what had happened because I had also attempted in this test to make a trial of other factors, tainting the certainty of my results.

So, I began a series of new tests of single factors:
1.jpg
Sanded oak with 2 coats thinned shellac. Shellac by itself certainly seems to blacken the grain. Is it blackening and staining it or just darkening it?

I made an extra heavy deposit in one spot:
2.jpg
Hideous! . . . so if the iron + tannin equals black stain idea applies, water isn’t the only vehicle for iron; iron contamination can come from shellac! Maybe the problem was just this particular batch(my everyday shop mix which is probably contaminated)?

I put some uncomtaminated shellac right next to it . . .and found it
Looked better, but I still see black spots ... will all my shellacs do this?

4.jpg
This is Zinsser clear shellac right out of my can(admittedly a couple years old). Very black grain.

5.jpg
Two pound cut of shop-made platina(stored in a glass jar). Iron effect much less pronounced here.

Is the problem with the lac in the shellac or the Denatured alcohol in the shellac?
Is it the denaturing agent? or would pure grain alcohol shellac behave the same way?

6.jpg
On the left 95% Clear Spring grain alcohol. On the right Klean Strip denatured alcohol. Definite black stain in both. So, seems like there is iron in the very alcohol I think of as being so clean. Can this be? Is the iron leached from the containers in which the alcohol is processed and stored? Is it actually iron causing this?

I did more reading. Decided to try bleaching the oak first. One author spoke of oxalic treatment as a way to re-nature the contents of the resin/tannin stuff in the grain so that it isn’t reactive in the same way to iron.

Started by sanding another section on the back of another table leaf, applying the oxalic acid solution, leaving overnight, and neutralizing the next day. (no picture) After drying, the area looked a lot brighter and cleaner and pinker, but every pore--examined with a loop-- now contained a chink of white material like shrunken caulking where the resin plug had once been. I then split the test area down the middle and scrubbed the left side with brass brush and denatured alcohol which removed the white chinks.

Next, I applied a stain(fiber reactive dye, water, and alcohol) on both sides. (not shown)

8.jpg
Right side, showing white residue from oxalic treatment.

9.jpg
Left side, white residue scrubbed out

11.jpg
Oxalic bleached sample after stain, filling, sanding back of filler, and 4 light coats of french polish(dilute shellac padded on). I like the light color and the lack of black grain stain, but the yellow dye/stain(which contained no heavy VOCs to make it really penetrate) sanded off when I cut back the filler yielding blotchiness.

If anyone knows how to avoid sanding off the stain underneath when I cut back the filler, I would be very grateful for the advice.

Now, it's time to leave this playground behind by turning the clients table right-side-up, where more than information can be gained through my efforts. ; )

[John TenEyck]

Wow, Anne, that was quite a lot of work you did. It seems to me that you deviated from your desire for a non-toxic approach, however, when you went down the oxalic acid path. It's not the worst stuff in the world, but it's far worse than an oil based filler. I think if you just stripped the old finish and used an oil based filler you could avoid the whole issue. Just sayin'.

[Anne Schmidt]

I had a feeling someone was going to say that! I know the dried crystals are not to be breathed, but I don't know how it is toxic other than that. You know something I don't?

[John TenEyck]

I had a feeling someone was going to say that! I know the dried crystals are not to be breathed, but I don't know how it is toxic other than that. You know something I don't?

No, no extra knowledge. The harm that oxalic acid can cause can be pretty severe, so you wear a respirator when you brush it out of the wood pores. Then what? You make sure to vacuum up - uh, no, can't do that unless you've got a HEPA vacuum cleaner. The solvents used in most oil based fillers are pretty safe with only occassional exposure, and they don't hang around. I'm not the world's most safety conscious person, to be sure, but using oxalic acid just seems like a bad idea in the quest for a non-toxic finishing process.

[Peter Clark]

Anne-
A few thoughts occur to me after reading about your experiments. I understand that Alcohol is used as a water wetter in automotive fuel systems. It makes the water suspend in the fuel better so it will burn without problems. My thought is that the Alcohol has a high % of water in it. My next thought was that Oak has naturally occurring silicates in the open grain. Maybe there are trace amounts of Iron suspended in the silicates. Add water from the Alcohol and presto- you have blue stain!