How can I determine what finish is already on the furniture?

This is very important for should you apply the wrong coating, you could come up against some serious adhesion problems, as not all finishes can sit easily on top of each other and therefore, it is very important to get this process right as it could save you a lot of problems further down the line.

French polished surfaces:

Well, to find out if the surface is French polished?  Or not you will need to carry out some tests.  Firstly you will need to apply some Methylated spirits to an unobtrusive area of the furniture, once applied the surface should become tacky if it does feel sticky to the touch then you have determined that the surface is French polished and can now be polished over with further rubbers as required.

Lacquered surfaces:

Well, you will need to carry out the same as above only using Cellulose thinners and once again if the surface becomes tacky to the touch then you know that you have a lacquered surface and can safely go over with additional coats of lacquer.

Varnished surfaces:

Once again the same process as above only this time you will need to use White spirits or Turpentine lookout to see if the surface starts to soften and if it does you can be sure that you have identified that you have a varnished surface on which to apply additional coats as required.

However, if you are still unable to decide what finish you have to work on, I would suggest that you strip off the old surface and then you can be sure that you know what product and finish you are applying, and in doing so will avoid any risk of product incompatibility.

Well, I hope that this will be of some help to you, as and when you have to identify the various finishes.

Feedback is most welcome!

This table hand French polished using a rubber & shellac.