Saturday, 23 July 2011

Red Wooden Heart - French Polishing

The heart will go from bare wood to shiny red!
Now for the fun part - making it shiny!!

By now you should have a 3D heart with all the major sanding done and only surface finishing left to complete.

For the finishing, you will need:
  • The sanding sealer and shellac that you mixed up previously - the recipe and blog post is here.
  • A small dispenser bottle for the shellac , like an eye dropper bottle, (some pharmacies sell them, but it’s not 100% necessary)
  • Fine sandpaper (at least 320 grit) for your orbital sander and sanding block
  • The tack cloths and OOOO wire wool mentioned previously.
  • A clean white cloth or brush for applying the sanding sealer.
  • A small amount of wool or cotton, some 6inch x 6inch pieces of soft cotton (an old t-shirt) for your muneca, and a glass jar with a lid for storing it in.
  • A dust mask for the sanding.
  • Possibly: alcohol (no, not for drinking), FFFF-grade pumice, a salt shaker, pure oil (e.g. Olive oil)

Applying Sanding Sealer
Now it’s time to break out the sanding sealer! Using a clean white cloth or an old brush, apply all over the surface. Pretty hard to do both sides at once unless you’ve found a way to levitate it, so do one side at a time. Let it soak in for 30 seconds or so and wipe off any excess.

When it’s dry (you won’t have to wait long), sand lightly with 320 grit sand paper, or the finest you have, still using your orbital sander. The goal isn’t to remove lots of surface material but just to knock back the grain.

Apply more sanding sealer, let it dry and hand sand from this point on. It’s best to use a sanding block for the flatter bits of the heart, otherwise they might come out a bit uneven.

A new muneca ready to be charged, an old one, and a storage jar.
Make your Muneca!
This is how we’re going to apply the shellac to the heart. The muneca is a wool or cotton core surrounded by a cotton cloth – it’s best if they’re both white, but as long as the dye won’t run when mixed with the meths, then it’ll be fine.

You’re supposed to use real wool to help the proper distribution of the shellac, but I didn’t have any, so cotton wool was a good substitute (I can hear the purists screaming!). A lot of people seem to use old t-shirts for the outside of the muneca, but I used a scrap of soft white cotton fabric.

Put a tight ball of wool (about an inch in diameter, once squeezed tight) in the middle of a 6in x 6in square of soft cotton (old t-shirt fabric is perfect) and gather the corners together so the wool is trapped inside. The inner core will act as a reservoir to dispense the shellac, which is applied to the inside wool core, and squeezed out from the contact pressure with the surface of the work-piece.

Shellac can be a sticky thing to apply and a lot of folks that are masters of French Polishing and make beautiful guitars & furniture recommend that you add a couple of drops of pure oil to the outside of the muneca to assist the application - The oil helps it glide over the surface of the wood.

I’d read that the oil rises to the surface and then needs to be removed by alcohol before moving onto to applying the next layer of shellac, so I decided to see what happened if I left this bit out. All in the nature of experimenting you understand... I found the first 8 coats or so to be very easy to apply, and only after that did I experience the muneca sticking a little bit. I guess on balance, don’t mess with the experts, but if your object is small or an odd shape (i.e. not smooth and flat) then you can probably avoid adding oil.

Shellac Sealing Coat
Wipe the surface dust off with a tack cloth. This is to remove any surface dust so that it’s not trapped under subsequent layers.

To begin applying the sealing coat, make the core of your muneca moderately damp with shellac by applying a good few drops of your 2lb cut. You don’t want to saturate it – too much is not a good thing here! Fold up the corners and slightly twist the end in the outer fabric to make it easier to hold.

Tap it on the back of your hand to evenly distribute the shellac through the core, and then tap on a piece of paper to make sure you haven’t put too much in. You don’t want to leave a puddle of shellac on your wood – the idea is to apply lots of very fine thin layers that amalgamate together.

These first few layers are to act as a base for the rest of the shellac and should be applied along the grain of the wood. I started in the middle at the top and ended at the tip of the heart. You should keep your pad moving the whole time – avoid pausing at the start and finish points, many people recommend a landing and taking off action, like an aeroplane, to start and stop.

Use less pressure when the pad is wetter and more pressure as it runs dry. Replenish with a few more drops of shellac as it dries out.

Wait a few minutes between coats and apply 3 of these ‘sealing’ coats in total. Now, store your pad in a sealed jar and leave your piece to dry thoroughly.

Layering up the first few coats of shellac on the heart.

Using pumice (or not) to fill the grain
Some woods (e.g. rosewood) need to have their grain filled at this point, and this is what I would definitely do if I were using ‘real’ wood (with an open grain) instead of just plywood. As it was, I just rubbed down the surface in between coats using wire wool and I still got a pretty shiny finish.

Obviously this isn’t a purist’s project, as I tend to like to experiment, but if you want a beautiful glass-like finish, instead of one that’s just really shiny, then this is how you achieve it:

You’ll need some FFFF-grade pumice in a salt shaker, a new pad cover, some pure oil (olive is fine) and some alcohol.

Replace your pad cover, add 8-10 drops of alcohol to the core and shake a small amount of pumice onto the surface of the pad. Never apply pumice directly to the wood.

Using random circular motions, work the pumice into the grain, covering a small area at a time. Reapply pumice and alcohol when necessary – you will begin to see a real difference in the surface of the wood. This stage is finished when you’ve gone over all the areas and the grain is filled and the surface smooth.

I might still go back and do this stage just to see what happens – it’s never too late to fill the grain!

You can see the colour and shine developing.

The true French Polish bit
So if you have indulged in filling the grain properly (unlike me, being a renegade), you’ll need to replace the cover on your muneca pad. Add some 2lb cut shellac to the inner core, just like for the sealing coats, and after tapping it on the back of your hand and a piece of paper (like you should every time you re-charge it), start to apply it to the surface of your piece in random movements.

Don’t go with the grain this time, just move the pad all over without pausing or stopping on the surface. The idea is to apply lots of thin layers that will knit together, and the random-ness of your movements helps this. Some people use a figure-of-eight, or oval shape to move their pad in, and I don’t think it matters as long as there’s an even coating on all bits at the end of the day.

I rubbed mine down with wire wool in-between the first few coats, followed by a wipe with a tack cloth to remove surface dust.

You can apply quite a few thin coats at once, but then you should leave it a few hours to properly dry. If you are experiencing the sticky-ness problem and have been using a few drops of olive oil to lubricate your pad, then you should wipe the surface of your piece with alcohol to remove the oil before commencing with the next polishing session. Just charge the core of your pad with a few drops of alcohol and stroking along the grain is fine. This application of alcohol is called Spiriting.

You might have guessed by now that the trick here is LAYERING. A really good shiny finish is made by lots and lots of thin layers of shellac.

So you should repeat the application of layers of shellac, followed by spiriting if necessary, until you get the finish you want. You can see it develop quite quickly, but as you have to leave it between sessions the whole process can take a week or more.

The last few coats develop a deep richness to the colour and shine.
I was happy after about 20 coats, but I lost track of exactly how many coats I applied – it’s easy to get addicted to the shine and the amount of coats becomes irrelevant. Just a few more coats, and it will be perfect…

I considered my heart finished after a good few layers of this last stage, but some people make it even more shiny by applying a few coats of a weaker cut of shellac, a 1lb cut is not unusual. There's lots of different recipes and techniques and more details can be found here:

And there's a great French Polishing trouble shooting/ Q & A guide here (with specific reference to guitar-making):

The finished heart!