Grain filling after an oil finish?

[HappyPixie]

My first attempt at turning was a shallow bowl in what I believe to be mahogany. I sanded through the grits to 320 and then used wire wool. Then I applied about five or six coats of tung oil. Rubbed on using a cloth, left 10 mins and any obvious excess rubbed off. Left 24hrs between coats. It ended a little tacky and I left if for a fortnight high above a radiator to cure. No longer sticky but quite matt and when reflecting light, some areas of the grain reflect light and other areas are very dull. As well, there are lots of tiny pock marks. Under a jewellers loupe these are obviously part of the grain. Now that the piece is finished - in several senses - can I go back and grain fill? If I do would I be able to put a final coat of Danish oil on top to give a mild sheen?
Cheers
Steve

 

[mrpercysnodgrass]

Why did you use Tung oil? Is it because you are going to put foodstuff into the bowl? If not you will be better off using Danish oil which has a higher build and will dry in four hours or so.
You could try grain filling again but I doubt it will stick now the grain has some oil in it.
Try sanding again with 400 grit and then apply more oil, eventually filling the grain with the oil.
The difference between some areas reflecting light and other areas being dull is the difference between long grain and end grain. The oil will have filled the grain on the long grain therefore reflecting the light and the end grain areas will have absorbed the oil and will require more oil than the long grain areas before full. That said you will still get shaded areas with the grain completely full all over because the long grain reflects light and end grain absorbs it but that is what makes wood so interesting to look at

 

[MIGNAL]

The Tung Oil will dry. No need to put it above a radiator, Oil finishes dry by polymerisation and not evaporation. You would be better off putting it in a window that receives indirect sunlight.
You will be able to grain fill. The only problem is that you may now get a slightly patchy result but it may work out fine. Hard to say.
My approach is to use some sort of Oil based finish direct on the wood. Something like Tung Oil or Danish Oil, I'll give it a few applications. That 'pops' the grain. Let it all dry. Then apply a water based grain filler. I make my own from egg white, Gypsum, water soluble glue and a dye to go with the wood. You want the filler in the pores, not sat on the surface of the wood. Like most fillers it will sink over a day or so. You may have to reapply the filler. After the grain is filled you can continue to apply your Oil finish.

 

[HappyPixie]

Yes, I chose Tung oil because I plan to use it for food. It sounds like grain filling might require complicated processes and/or mixing of bizarre things. Someone suggested to me that I sand using oil and create a slurry. Presumably I'd let that dry in the grain pits and then use fine grit wet and dry to skim off the surface leaving the dried slurry in the cavities. Has anyone got any experience or advice about this strategy or are the other grain filling suggestions above the best options?
Thanks to both.
Steve

 

[MIGNAL]

Yes, that's another method. Probably better off using Danish Oil for that. Sand using something like 180 or 240 Grit with the grain. You sand with the Oil 'wet' on the wood. Occasionally add a few drops of Oil to the surface of Wet/Dry. Any excess you get wipe off with a rag going across the grain. It's a bit messy. Again it will shrink back somewhat. It does take longer to dry because the Oil slurry that is in the pores is relatively thick, much thicker than a coat of varnish. Give it at least 3 days between applications. Water based fillers dry much more rapidly. Then there are the ready mixed paste Oil based fillers that come in various tints - messy, strong solvent smell. There is also the pumice method that is used with Shellac. They all work but filling grain to a high level of perfection is no easy task.
Don't forget about the safety with rags and Oil.

 

[HappyPixie]

Thanks for the advice, Mignal. Good sense about sand with grain and wipe off across. I'm always careful about oil and rags - too many inflammables nearby to risk anything spontaneous.
I have several more pieces of the same wood so I think I'll try the slower slurry method on this one and do more research on the pastes before I need to fill the next one that I make.
Cheers
Steve