In my experiences with cable it requires a much deeper etch than damascus because all the steel is the same. The pattern you end up with is due to the individual forge welds that take place between each of the many strands. I have heard this referred to as de-carb lines. I have used ferric chloride in many different dilutions with water, the strongest being 50/50, as well as using vinegar and ferric mixed 50/50 I have done it for hours taking it out every ten minutes or so to remove the oxidation, I was told the black looking oxidation hampers the etching process. I have found that muriatic acid is much quicker and if you heat it first to about 140 degrees F it gives you a totally different look, as well as makes it work even quicker. This is some nasty stuff though, due to getting it on your skin as well as breathing the fumes so I would not recommend it unless you are familiar with working around such harmful materials. I usually set a glass container inside another container that contains heated water. To me a deep etch on cable looks better than a shallow etch. I am sure what you were using would do just as well it just takes time. Make sure there is not any oil on it before you start etching.
LDW