Adhesion Problems with Gold Leaf and Nitrocellulose

      A finisher looks for ideas to improve gold leaf performance. April 16, 2010

Question
I have an adhesion problem in my gold finish.

The finishing process is:
1. Base coat (red color)
2. Sealer
3. Gold leaf
4. Sealer
5. Gold leaf (to touch up the missed area)
6. Sealer
7. Glaze
8. Topcoat

The sealer and topcoat are nitrocellulose. But after it dries, the gold is easily chipped off. Any ideas?

Forum Responses
(Finishing Forum)
From contributor R:
You should use a dewaxed shellac or a 2k isolante urethane over the gold for good adhesion.



From contributor T:
1. Base coat - what material? (lacquer, enamel, etc)
2. Sealer - sanding sealer?
3. Gold leaf - real gold? Applied over sealer with what adhesive?
5. Gold leaf - same as 3.
7. Glaze - what medium?
8. Topcoat - real gold needs no top coat unless it will be handled frequently. Same for most antiquing glazes. If imitation gold leaf, dewaxed shellac is suggested before any other topcoat. And you need to make samples before real projects.


From contributor B:
I had this same problem with almost the same finishing schedule. I have been using Rolco Urethane Topcoat. It can be misted on or built up pretty thick and it is specifically designed for use over leafing. It is a bit expensive, though, at around $20 per quart, and I can't find any larger size than a quart. It comes in satin and gloss only, but with steel wool you can achieve other sheens in between.

Also, I prefer to gold leaf right on the red primer, not on top of a sealer of any kind, except for small touchups after the first coat of the Rolco.

To clarify, Rolco was the answer to my problem, not part of the problem. Before, when I had chipping issues, I was using nitro lacquer, conversion varnish, and shellac, with none of them helping.



From the original questioner:
My finishing system is nitrocellulose - all coating materials (base coat, sealer and top coat) are nitrocellulose. The gold is gold leaf. I use gold leaf sizing (water based glue) to stick the leaf over the sealer. Thanks - I will try the dewaxed shellac.


From contributor C:
From one who has used just about everything for gold leaf and does both traditional style water gilding and matte gilding, use of lacquer is tricky to say the least. Lacquer offgasses for over a month after application. These gasses are the slow solvents that make up a small percentage (usually less than 3%) of the coating formula. Whether you use solvent base or water base size, this offgassing will affect the coating's hardness. The quicker you apply the gold over the lacquer, the more it will be affected.

The other thing you're fighting is the shrinkage of the coating over that period of time, if you don't allow at least 30 days for all of it to take place. This means movement under the gold - not a good thing!

It's usually at its worst when people in a hurry apply the gold over a fresh coat of nitro or any other evaporative finish, even acrylic. Haste makes waste. So now you have two problems - a size being affected by offgassing and a film which is in movement due to shrinkage.

You also have to consider that the size is not an evaporative finish, therefore you have to sand the lacquer with fine paper (600 grit) for the size to have good long term adhesion. For flat surfaces this is not a problem - for ornate surfaces, it's a pain!

The size has a lot of elasticity for the first few days after application, then it starts to harden and get brittle. Some will say that gold size will stick to glass, so why the sanding? Glass contracts and expands very little compared to lacquer. And it takes a lot more heat or cold to do so. Even metal is a better foundation than wood and lacquer. Contrary to what you may have been told, gold size is not a glue; it's a varnish. On a properly prepared, cured surface it will adhere extremely well. If not, it won't!

Another point is nitro will yellow with time, which is why I prefer acrylic lacquers for 100 percent acrylic coatings, if for an interior use. 2K urethane if exterior. Gold will only look its best with gloss coatings.

As someone else already pointed out, if it's not going to be handled much, there is no need to coat at all. So, let the lacquer cure totally before applying the leaf. This will most likely eliminate your problem, and if not, follow the other steps outlined.



From the original questioner:
Thanks. The fact is we do not have much time to do the finishing. We want to finish the job in a day or less if possible.


From contributor C:
Then you will have to put up with the chipping problem.

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