Replies

1. 
   Drew_Nyman | Jul 26, 2000 10:49am | #1

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   Jay; You might try applying a solution of tannic acid first.I suspect you already know this but you can reverse the process with oxcalic acid. Drew

1. 
   Jay_Stallman | Jul 27, 2000 01:30am | #2

   *Drew,Can you supply more details on the use of the tannic acid or oxalic acid? Concentrations, method of application and suppliers? Are you suggesting that the oxalic acid will lighten up the color of the mahogany back to its original (ie un-stain it?) Does the tannic acid promote even uptake of the potassium dichromate? How would one predict the need to pre-treat with tannic acid. As I mentioned the potassium dichromate worked great on all but one board (unfortunately, the top) It was fine on solid wood and crotch, but irregular only on the straight grain veneer. Thanks for the advice.Jay

1. 
   Rob_Millard | Jul 27, 2000 03:46am | #3

   *While I can’t help you fix this project, I can tell you a way that has work for me to color mahogany. I have used potassium dichromate, to color inlayed furniture, which is my specialty, but the potential health concerns forced me to find an alternative. I tried lye, which was very effective. Now I use hydrated lime, its easy to use, does not raise the grain like the lye did, and is fairly forgiving. Right now I making a reproduction federal secretary, that has some crotch veneer. This particular veneer is very dark, but by varying the concentrations of the lime to water, I will be able to blend it in. The color can also be tweaked with Trans Tint dyes in oil (green to make it more brown, etc.) I wouldn’t bother to use the lime for furniture that wasn’t inlayed, aniline dyes, and NGR dyes are so effective, there is no reason not to use them.One thing lime won't do, that aniline dyes will, is take over hide glue. Any spots of hide glue left on the surface will show just like white or yellow glues do when you stain over them.So I always wipe my projects down with mineral spirits first to find any problem areas.

1. 
   Chuck_Probst | Jul 27, 2000 08:24pm | #4

   *Jay: I'm wondering if the hide glue bled through the veneer enough in some places to interfere with the absorption of the potassium dichromate? If you use a veneering hammer, the hide glue can actually ooze right through thin, porous veneers. If you use cauls to clamp the veneer into place, the glue can absorb through at the point of pressure. A pattern to the absorption may be obvious enough to tell you if that's what happened.I use thinned hot hide glue on the end grain of mahogany turnings, in order to block the absorption of potassium dichromate and keep the color more even overall. Maybe you got the same effect,inadvertantly. Just guessing here. I wouldn't know quite how to correct the problem you have. Possibly a gentle wash with clear water over the lighter areas, to remove some of the glue from the pores of the veneer? Probably be best to veneer a piece of scrap and give that a try.

1. 
   Jay_Stallman | Jul 30, 2000 05:20am | #5

   *Thanks. I suspect you could be right, although with hide glue you intentionally apply the glue to both the front and back surfaces, to lubricate the veneer hammer. It does get scraped off, and sanded, but it's in the pores. This should be uniform. I used a vacuum bag to press the veneer, so no pattern was evident. Also the same process didn't interfere with the uptake on crotch veneer, which also had the glue in the pores.

2. 
   Michael_D_Foscone | Aug 19, 2000 12:12pm | #6

   *Hi; Well potassium dichominate is a very difficult chemical to apply by your method. The only fool proofone I used and it was many years ago,(because I stopped using a chemical when I found I can get more consistent results with NGR stains)was to spray it on. You probably could fix your mistakes by toning over them with more potassium dichrominate,just allow a tiny bit to come out of the gun at a time,and it will dry on contact. This is of course assuming you have spray eguipment,if not I doubt you can fix it.

3. 
   Rand_Bardsley | Nov 17, 2000 04:23am | #7

   *Does anyone have experience treating pine with potassium dichominate? Should I use Tannin acid before? What would be the color or results be either way? Does anyone have experience with nitric acid? How would those results compare? How about ferric oxide? Will they all produce different shades of brown? Why would you use one over another?Any information would be appreciated. I am making a farmers dining table out of 5/4 pine and want to end up with an antique finish with a rich old looking patina. Thanks for any help.Rand