searching for good film forming alternatives to lead white

This is an excellent question as it comes at a time when the conservation community has only relatively recently begun to explore the mechanisms behind problems associated with zinc white bound in oil and/or alkyd paints (note that to date none of these problems have been encountered in acrylic, watercolor, casein, or distemper paints…or in frescoes). By recently I mean over the last 20 years or so. These issues may also arise in egg tempera paints although to a lesser degree however much more research is needed to confirm or disprove this. Back to your question regarding “what to do”? First, safflower, walnut, and poppy oil are all considered drying oils, meaning that they DO form dried films after a certain period. While the films themselves may not be as strong and/or durable as compared with linseed (particularly poppy and safflower), when any of these oils are mixed with lead white you avoid many of the issues you cited above. I would not have any issues with using walnut oil either. Second, zinc white itself does not really act upon titanium or lead white pigments…it acts on the fatty acids present in the oil or alkyd binder. But certainly issues have been observed even when zinc white is mixed together in small quantities with titanium or lead (studies performed by Marion Mecklenburg, published in 2008). However, I am also one to state that in conservation we are very prone to basing everything on one single study, which from a scientific standpoint is not always the best approach. This is mostly due to the fact that we have limited resources (meaning funding) as a field. Studies focusing on zinc white need to be repeated in order to truly confirm some of these findings (not that I disagree with them outright by any means). That being said there are really no “best painting practices” alternatives at the moment…until the paint industry and/or conservators and scientists are able and/or willing to perform additional tests we will simply have to wait. In the meantime I would recommend using lead white bound in any of the oils you mentioned above (although walnut and linseed will certainly give you films that are more resilient). If that is not possible do not despair if you choose to use zinc white. The fact that you are using rigid supports is a very good thing and will certainly help to counteract any issues that may arise with brittleness. For the moment a good rule of thumb regarding zinc white is the less you use the better….but if that is not a good solution you can also simply record your use of zinc white and other materials on the reverse of your painting. This will give future conservators the information they will need when addressing how best to care for your painting should future issues arise (and if your painting is professionally executed and well cared for there may not be any issues!).

Unfortunately there is no consensus on whether one is less problematic than the other at this point in time. Therefore I think ultimately the choice is really up to you as an artist…weighing in aesthetic appearance as well as the handling characteristics. Your questions indicate that you have already done due diligence in terms of researching these problems that the paint industry and conservation are just now tackling so you should feel very good about that…when more research has been done regarding zinc white/titanium white you can be sure that we will be posting up-to-date information in our resources section. As for your question regarding octanoic acid, this is likely added to serve as a drier. Contrary to popular belief, lead white does not dry that fast…it just dries very “well,” forming a very resilient film. Litharge and red lead on the other hand will dry very fast when added to oil mediums. Driers are not advisable when used in excessive amounts. While the amount of drier present in a commercially available can be difficult to judge, most likely a given manufacturer will add just enough to promote a more consistent drying rate across an entire paint line OR to create a paint that is specifically being advertised as “fast drying.” What is often more problematic concerning driers is when artists use them in their palette cup like a diluent or a medium. When this technique is employed, one will invariably introduce far too much drier into their paints, likely leading to problems down the road.

Thanks for your response. I would like to clarify a few assertions and discuss a couple of things.
First, let me make clear, I believe that if you take the necessary health precautions, can afford it, and dispose of the waste appropriately; lead white is a vastly superior white pigment for painting in oil. I am not even diametrically opposed to making the lead white oneself IF one follows responsible health and environmental protocols.
The production of lead white needs to involve many precautions to protect the health of the operator. You have to make sure to use gloves and a respirator, facts that the Master’s Pigments channel now mention in text, if not always in practice, on their video. I watched this video practically the day it came out, and the current version it has been modified to seem less cavalier with about health and the environment, despite still showing the maker using his bare hands to break up lumps of lead white. Another important aspect of safety is to make sure that no stray particles of lead white drift onto adjacent surfaces where they will pose a future risk.
My real issue with the video and their procedure in general is the irresponsible method they use to clean the pigment. It has now been edited from the video, but the original post showed them washing the white lead and pouring the wash water down the sink drain. This wash water contains not only smaller particles of white lead, but all of the water soluble lead products that were not converted to insoluble lead carbonate and related side products. A major component of this would be lead acetate, one of the intermediary compounds. This dangerous, poisonous chemical is easily absorbed into the body and is very hazardous for people and the environment. I posed these concerns on their Youtube channel and they disabled user comments within a day or two. I do not know for sure that my comments were the reason but I have my suspicions. They has since edited out the portion of the video showing them pouring out the wash water, but the remaining portions suggest that this is still their procedure and they are just no longer showing it. No matter what, they make no mention of how to properly dispose of the contaminated water. This could really only be done by using a closed system like that used by few others in the business. On a small scale like that shown in the video, one would need to take the contaminated water to a municipal or private hazardous waste disposal firm. In short, while I am not opposed to having artists make their own lead white, it is very difficult to do ethically and doing it properly would likely costs as much or more than buying it.
As to Louis Velasquez and his assertions. I do not take real issue with the use of sun clarified and thickened linseed oil (or FLAX OIL as he reiterates so many times in his book) mixed with calcite as a medium. This is probably a fine procedure and is certainly preferable to the soft resin mediums so common in 19th and 20-century oil painting practice. The issue is the authority and conclusions drawn in his literature. He joins a long list of writers who have “discovered some lost secret of the masters”. Like Jacques Maroger, Donald Fels and others, he takes a few snippets of text from historical treaties and then extrapolates a “reconstruction” of the materials and working methods of the greats from history.  
So what evidence is there? Certainly, water washing cold-pressed oil was practiced in the past. It was one of a few ways to refine drying oils. Heating, and letting the oil set for long periods of time (the actual origin of the term stand oil) are others. Most of these processes were intended to make the oil drop its “foot” or the mucilage and other water-friendly impurities. Earlier practitioners appear to have understood that impurities in oil do contribute to some of the eventual yellowing. This has been confirmed by modern scientific studies. The question is if Louis Velasquez’s method is superior and lives up to his assertions. We do have to keep in mind that he is not a scientist, a scholar of codicology, or a technical researcher/conservator.
First, it is erroneous to suggest that oil purified by a particular process does not yellow (including healthfood store “FLAX” oil and commercially available linseed oil). All of the drying oils used for oil paint yellow, some yellow a little more or less and others do so more or less quickly. In fact, evidence suggests that even walnut and poppy seed oil eventually yellow to a similar degree as linseed oil. Washed and thickened/bleached oils are more acidic than unprocessed oils. This does make them more effective at binding a given amount of pigment as compared to the same oil before washing. This is practically moot today, though. Modern processing of linseed oil can create a product with fewer impurities than can be done by hand on a small scale. One can purchase alkali refined oils in a whole range of acid numbers for a given task. There is really no evidence at all that water-washed cold-pressed linseed oil is superior to a quality alkali refined linseed oil made for the particular purpose at hand (binding paint, medium additive, various viscosities, etc). I would generally caution people to do numerous tests on FLAX oil purchased from healthfood stores as oil made for human consumption and is often grown and cultivated to contain greater amounts of components thought of as health beneficial, rather than making an oil optimized for binding paint.  In the end, I believe that it  would be fine to paint with the oils made by Mr. Velasquez’s process as long as the original oil was of a good quality, but I can see no reason to consider it superior to high quality commercially available materials.
I am going to keep the section on calcite very short. Yes, calcite has been found in the whites and other colors used by Diego Velasquez, Rembrandt, and others. Chalk/cacite was a common adulterant/filler in lead white of the era. It is practically impossible to determine whether the artist specifically added calcite to their oil. They may have done so for the purpose of adding translucency and/or specific rheological properties, or it may have simply been already in the available lead white. Remember that despite the romantic notion that artists of the 17th century made or had an assistant make all of their materials specifically for them, almost everything that an artist needed to make a painting was available for purchase in the 1600s.

It is likely that titanium white bound in alkyd may serve as an adequate substitute for lead white bound in oil and/or alkyd…however as per this thread as well as others on the forum it is again important to realize that not all alkyds are created equal. I suspect you may have to purchase a few different brands and test them out first. The main problem with certain lines of alkyd paints is that they can be inherently fatter…while others (Gamblin’s comes to mind) are deliberately made to be leaner, allowing the artist to incrementally add more alkyd medium to the desired consistency. As for whether you can use a Ti/Zn combo in alkyd, I am afraid that not enough testing has been done yet to confirm whether you would be able to avoid the inherent vices that can occur when dealing with an oil binder…alkyds are chemically similar to oils and it is certainly possible that any free fatty acids that remain in the film will interact with the zinc white. The same can be said of Kremer’s Strontium Ti white….we have not had the pleasure of playing around with this pigment and so have no idea whether it would form an oil film that could serve as a satisfactory substitute for lead white.