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Discolouration of light timber by adjacent dark timber during sanding and finishing.

PenMaker22

Registered
Joined
May 29, 2020
Posts
1
Location
Australia
First Name
Scott
Hi Everyone,

I sometimes make pens with glued sections of timber. One that I particularly like is, for example, maple bands in ebony, or vice versa. However, I often find that the darker timber discolours the lighter timber, making it beige or, even worse, just a dirty grey colour.

Does anyone have any tips to prevent that happening?

Cheers.
 

flexi

Executive Member
Joined
Sep 12, 2014
Posts
6,159
Location
Maidstone
First Name
mark
Is this when sanding??
I have used loads of segmented blanks and once the glue is dried they are very stable....the only way they discolour is very fine dust from sanding and a quick wipe down with boiled linseed oil generally removes it....
Hope this helps:thumbs:
 

Margo

Full Member
Joined
May 25, 2020
Posts
73
Location
England
First Name
Margo
I've read (somewhere!) to use sanding sealer between each and every grit when sanding to reduce discolouration.

I've tried it, but only once!
 

Pierre

Graduate Member
Joined
Sep 2, 2015
Posts
996
Location
Southern Central France
First Name
Pierre
Hi Everyone,

I sometimes make pens with glued sections of timber. One that I particularly like is, for example, maple bands in ebony, or vice versa. However, I often find that the darker timber discolours the lighter timber, making it beige or, even worse, just a dirty grey colour.

Does anyone have any tips to prevent that happening?

Cheers.

Hi Scott and welcome,

Are you using wet and dry? Many people advocate wet sanding, I have never found this to work but I do tend to work in the spring/summer where my temperatures hit up to 42 degrees so wet sanding can drag staining. Equally some glues take more than 24 hours to dry even though they may be classified as 15 mins 30 mins 2 hours etc I let all of my glues dry for at least 24 hours and sometimes 2 days because they also can allow dust drag into the lighter wood, ie the glue is still damp and sticking to the dust. Actually it goes into both woods but you cant see it so well into the darker wood. Finally, some glues can take the stain in the darker wood and by osmosis into the cells they can transfer the pigment, so you need to control the glue. For wood on wood I use normal PVA white, for wood on pen tubes I use gorilla (but that is hidden) and for wood on aluminium I use medium CA and let it cure for 48 hours. I have found that using yellow PVA can give the appearance of pigment transfer but in fact it is the PVA that is causing the colour change, but I haven't used that in the last 5 years so they may have changed the formula over time.

Dont forget that some dense exotic woods have their own oils like lignum vitae and azobe or Niangon and these oils themselves transfer their colour but that can be overcome with a drop of acetone (yes one drop on a cloth for a pen sized object more for a bowl) to remove the surface oil because the discoloration is only on the surface. With these types of oil, they are a bit greasy like coronavirus, so I would think that a drop of alcohol (Ie same strength as hand sanitizer 60% proof) would work as well; use it as you would a sanding sealer. (note I havent had to try that yet but logic comes to mind from a past life in biological stuff).
 

Bill Mooney

Blind old git
Grand Master
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Aug 16, 2014
Posts
10,997
Location
County Durham
First Name
Bill
As Margo says, sanding sealer before sanding with each grit stops the dark timber bleeding into the light timber. I always do it without a problem.
 

Margo

Full Member
Joined
May 25, 2020
Posts
73
Location
England
First Name
Margo
So here's a kind of related question - can grubby, red-stained tack cloth be revived?
 

Phil Dart

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Executive Member
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Nov 28, 2014
Posts
5,455
Location
Colebrooke, Devon
First Name
Phil
No, but I find that tack cloths tend to keep their dirt to themselves. As long as there is still a bit of "tack" to it, it should still do the job. You have to take a reasonable view about it though - if it's filthy you'll need to replace it.
 
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