The apparent inability of carbon-based preservatives to move into and protect checks exposing untreated wood in service means it may be more important to achieve deep penetration with these preservatives. The work reported here builds on previous research which examined the effect of a range of pressure treatment process modifications and formulation additives to improve the penetration of borate- and copper-based preservatives. The effects on penetration of carbon-based preservative of six process variables and three additives were evaluated in the new, insulated stainless steel retort. Fluctuating pressure around a set point did not improve uptake or penetration. Increasing solution temperature showed improved uptake, but did not improve penetration. This was likely due to the increased fixation rate of the DDACarb/Amine oxide. Steaming before treatment in kiln or in retort impeded uptake and penetration. Steaming after treatment also did not show improvement over the standard treatment. Adding ethanol did not improve uptake or penetration. CCA reference treatment showed the greatest uptakes suggesting that the carbon-based preservative may have a negative effect on uptake. Adding DOT at 0.5% to the treating solution showed an improved uptake of 16%, but penetrations were less than the standard treatment, possibly due to stripping of the amine oxide during previous treatments. This requires further investigation. Comparing the penetration of borate and DDACarb/Amine-oxide showed that the DDACarb/Amine-Oxide component of the treating solution was being stripped out of solution as the formulation penetrated the wood. Additive A showed the most promising improvements increasing edge penetration by 16% and increased heartwood face penetration by 22%. This treatment had 85% of the samples greater than or above 5mm surpassing the CSA standard for residential product group C, without incising.