Doug, it's says on fleabag that they have been pressure treated. However.... It's not really the pressure that will control the depth of colour, but the vacuum, if any, that it was subjected to and the length of time that it was held at that vacuum before the ammonia was released into the chamber and the pressure exerted. The surface colour of the wood looks good but, being suspicious, it could be misleading! The humidity level of the wood affects the reaction between the tannin in the oak and the ammonia. You can assist the fuming of a bowl by sanding it and then lightly spraying it with water to raise the grain and repeating the procedure. If you then put it in the fume cabinet (or airtight plastic box) when still damp, you can get a quicker fuming reaction.
If it hasn't got all the way through and you make a pen with a taper like a streamline, it's going to look pretty daft! I bought some 80/80 ammonia (ask mr google) for about a tenner and I've got loads left.
The info about the pressure vacuum system is as a result of the fire protection treatment we used to carry out to timber to make it a class 0 timber to bs476. We used to impregnate timber with a magnesium chloride solution to make it resistant to assisting the spread of flame (different from making it flame retardant). This work was carried out on 15mm and 20 mm thick profiles. Oak was one wood which was just on the bounds of feasibility for this treatment as at 660kg density it was barely viable to get 100% impregnation. This was after the vacuum had been applied for 20 minutes and then the pressure reversed for the same time. I have my doubts as to the successful colouration of the wood throughout, and would suggest that everyone would possibly be better off buying a bottle of 80/80, although if the wood is relatively recently felled, yet dry, some household ammonia can do the trick, particularly if the wood has been dampened.
But then again I could be wrong, again!
