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HOME/The Yellow Sport; Cracking the Colour Code

23 September 2011 by Harm Heuvelman

A paint-job can make or break a restoration project. It is after all the most eye catching aspect of every motorcycle. When restoring a classic Ducati, we are presented with a number of issues; how do we reconcile originality, good looks and modern technology. Especially in the case of the Ducati 750 Sport; the most difficult of them all: the ‘Yellow Sport’.

As always at Back to Classics we start out with the basics: how did Ducati paint their bikes when they were new? As was accustomed until the end of the 1970’s cars and motorcycles were painted with cellulose based paint such as DuPont Lucite. Cellulose paint can be applied under very simple conditions as it dries almost immediately. As cellulose paint doesn’t have a natural gloss, the individual parts were polished to give it a shine. Sometimes no lacquer finish was applied and decals were put on after polishing.

You can imagine that this finish leaves the bike unprotected from UV radiation or wear. This is why Ducati’s in their original paint don’t shine that much. Decals often are worn by the driver’s knees and elbows. And if someone parked the bike outside for some time, probably the left side of the bike has a different shade of colour than the right side.

This has nothing to do with the much heard statement that the paint on steel parts becomes different from paint on fibreglass parts. The paint surface has the same chemical properties on steel as it has on fibreglass. It’s just that the amount of UV radiation was different on the mudguard than it was on the fuel tank.

The wear of paint and decals can give the Ducati that nice patina look. Something that should be preserved if possible. However, how should we go about restoring if the bike is in a bad condition?

Restoring a Ducati to factory specifications presents a direct problem: cellulose paint is not allowed anymore. This means that we have to look for the best alternative. Every existing paint system uses a blank lacquer finish, which means that decals must go underneath it. Furthermore, most specialised companies are only allowed to use water based paint systems. Some disadvantages of these paint systems include long drying times, and limited toughness. The major disadvantage however is that it easily runs under the tape, so when painting two colours on the same part, a truly straight line is very hard to accomplish.

Back to Classics found a partner using the thinner based paint system DuPont Centari, for which special permits are needed. With a rather short drying time, it comes closest to the original cellulose paint. Of course, after applying up to six layers of blank lacquer, the gloss and depth of the paint is way better and not to compare with the original cellulose paint. But if we have to use a different system anyway, we feel we should pursue the highest quality available.

The thinner based paint system also gives us the possibility to spray the letters and stripes instead of using the original decals. It is even possible to make the surface that smooth that no relief can be felt when stroking the paint with your fingers. We feel that this goes too far. The use of decals, even if applied under the lacquer finish, remains closer to the original treatment, however we are open to argument regarding this statement…

Now that we have chosen a paint system, comes the issue of colour. Especially for yellow and red, it is very hard to retrieve the original colour as these will react most to UV radiation. As many original Ducati 750 Sports have been subject to UV radiation, the original colour is hard to find. And apart from that: we see many restored ones with the wrong colour!

It is too easy to think that even when you have the original colour available, you can easily pick a one from a range because you are comparing different systems. We have a New Old Stock side cover from a 750 Sport available as you can see on the pictures (the left one, picture is taken outside) that has been lying around in the original plastic in the dark for over 30 years. Here we have the ability to retrieve the original colour!

To find the matching colour for our thinner based system a process of trial and error is followed. As it has to resemble the original both in artificial and in natural light, many samples are created. After picking the best, we research even further until we found the matching recipe. Judge for yourself, but we feel we have cracked the colour code for the 750 Sport!

Tags: 750 S, Concours, Nut-and-Bolt Restoration, Patina Restoration

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