Firstly, a very big 'thank you' to all those who have sent messages on
this subject. Thanks to your input, I now know what I am doing!

In answering my question, several other questions have been asked so I
have done some research and can supply answers.

Firstly, in his reply on the 22nd of September Hans Van Oost said he was
unsure what the proportion of shellac was in French Polish. I contacted
Rustins Ltd of Cricklewood, London (who supply most of the major D.I.Y.
chain stores in the U.K. with wood care products) and asked them. After
a lot of deliberation, they eventually told me that their French Polish
solution contains approximately 23% shellac. Apparently, this is known
as a 'two pound mix'. By some calculation, I was able to work out that
it was about double the strength of the solution Hans suggested, so
would need diluting with an equal amount of meths. This, however, is an
extremely expensive way of doing it unless you need a very small
quantity for 'one-off' use - buying shellac flakes and meths and mixing
it yourself is much cheaper.

As regards ethanol (pure ["drinking"] alcohol for non-chemists), Hans
is right when he says it is very good to drink. For this reason, pure
ethanol is very difficult to get hold of and so methylated spirits is
used instead. In an attempt to stop people drinking it, the meths
available in the U.K.  has up to 15% methanol added to it (methanol
is similar to ethanol, but poisonous) and is coloured purple as a
warning. As a rough conversion, a litre of meths weighs about 800 grams
so the mixture Hans proposes is 125 grams of shellac in a litre of meths.

The question of whether to treat keyed music with shellac or not is a
vexed one and both the 'Yes' and 'No' camps have had their fair say. My
own view is that in this case I was asked to treat them (remember, the
customer is always right). I view shellac on music as like an insurance
policy - when music is cut for someone else's organ, you cannot
guarantee the keyframe condition or likely usage, so it makes sense to
make it as abuse-resistant as possible and trust it will never be
needed. If it is for your own organ, then the choice to shellac or not
is yours.

Again, many thanks to everyone for their input.

Jeremy Brice.
Watford, Hertfordshire. UK.