Decant enough Le T for the job into another container and give a quick squirt of propane from an (unlit) blowtorch or similar to displace the oxy before putting the lid back on the tin.
If you do get a skin you will need to strain the Le T into another container. I use muslin cheesecloth. Plastic pots with airtight seals are better than tins IMO.
A simple remedy which I have used successfully is to store the can upside-down, after making sure that the lid is secure, of course. If a skin does form, it will be underneath the varnish, which will then be at the top of the tin. Q.E.D. [Quite Easily Done] This applies to all paints, not just Le Tonkinois.
Peter.
The gas trick sounds interesting. I have tried all the others and they help but only to a point. Apart from the crazing problems (q.v.) it seems to be the biggest problem with the stuff.
Had the same problem with varnish once the tin had been opened. I tried co2 (mig welder gas ) to displace the 'air'. Next time I went to the tin it had imploded as the co2 had clearly been absorbed by the varnish. No skin on the varnish but a very odd shaped 3 litre tin. Almost impossible to open with the vacuum inside. I decide that decanting the rest into appropriately sized jars was better.
Woolworth's do a plastic tumbler with a screw-on lid that I find ideal for varnish or brush cleaner, etc. Only 99p. Look in their "Tupperware" section.
Store LeTonk in a squeezable plastic bottle, pour out as much as you need, then squeeze all air out of the bottle and replace cap without letting air back in. Bottle will be a wierd shape but as long as there is no air there will be no skin formation. I've got some that has lasted two years like this.