linseed oil cupped boards how to straighten

About 20 years ago my brother salvaged the wood from a pre-civil war farm house in rural north Georgia.
He saved one plank. Yesterday he told me that the plank which he thinks is pine and about 1/2 an inch thick was severely cupped and bent as a result of applying linseed oil to only one side. He would like to flatten the plank. His current thought is to apply linseed oil to the other side or try and use a solvent to remove the linseed oil (I told him that this would not work). I suggested either steambending it back or trying the old trick of laying it in the grass cupped side down on a sunny day.
What are his options for flattening what is probably and old growth plank that he would like to save...
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OK, the problem is that he only pu the oil on *one* side (wood that old should be stable by now - at least as stable as its gonna get, unless you change its environment).
the first thing I'd try (if you have the time) is to put linseed oil on the *other* side of the board - that way all the sides have the same barriers to moisture (the reason the board cupped is that with the oil on only one side, moisture could get in and out of the untreated side easier than the treated side, so the wood on the untreated side expand/copntracts more than the treated side). Once the oil is on, I'd wait a good bit (maybe as much as a year) to see if it flattens back out.
If the cup is severe (and the above doesn't work), I don't know of any way other than planing the cup out to get the board flat again.....
good luck
--JD

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