Isn't there a process whereby preservative is forced into the wood under pressure so that it penetrates more deeply into the wood? It isn't my area of expertise, but I do seem to recall hearing about that treatment.
Ron.
Tanalised timber, lots of fence panel suppliers claim their products have been pressure treated.....whether they have or not...
Tanalith C is the preservative and contains (or least it used to) arsenic and generally has a greenish hue, Tanalised isn't the treatment its the stuff they use
Depth of impregnation depends on, amongst other things, the process - single or double vacuum treated - most joinery grade timber, if needed treating, is vac vac treated, same sort of stuff but dries to a very light brown hue, expensive 3 day process if done to the letter (in, treat, correct dry times), however I used to drop stuff off at the old treatment plant in Barking before 8am on the way into London and pick it up before 4pm on the way home, still dripping wet in some cases.
Closer the grain of the timber the less the impregnation.
As most 'cheap' timber is generally a fast grown (south facing) redwood the treatment impregnates quite easily and quickly, when you get to North face 5ths and sawn falling it has to be vac vac treated to be effective