Dear MITRA conservators,
i want to ask if adding calcite into linseed oil as a paste medium does anything good in terms of improve oil film durability, flexibility? i heard it will form calcium metal soap with react of free acid that will degrade the oil film in long term, which had been evidenced in many old painting already? if that is true, should we completely avoid using calcite, instead using other more inert? or calcite actually improves film quality if optimum amount added, if so, what will be the optimal ratio?
Hello there,
First, thank you for proving the forum is still alive.
Whether calcite might impact the longevity of the film by forming soaps, I don’t know the details and someone more versed with this on the forum will say.
I would personally be surprised it’s ever so pronounced it becomes the predominant cause of defects for the ageing film. (and what defects?)
As for it to impart some mechanical advantage, I don’t see why this mineral would. The main flexibility of the linoleum will come from the oil, and any mineral filler to the right level will raise its pigment-volume concentration to reach more hardness of film eventually. It’s not mineral specific but a volume ratio between solid particles and vehicle. I’m not sure where the optimum would be if you actually need more hardness for your film.
Durability wise, it will depend if your film is more exposed to flexibility strain or mechanical shocks or chemical attacks. For the first and last, it’s best to refrain from adding more minerals to your work. A varnish later can give the protective hardness to support the durability of the oil film. So generally I’d advise against additions of minerals for this. Safer to use mediums if you want a different consistency.
I hope this gives you some food for thoughts, and that others will jump in to reply.
Have a nice day,
Latest Post: faster drying paint film due to driers or wax? Our newest member: htaletdntl Recent Posts Unread Posts
