Watermark Identification

Is there anyway of identifying watermarks beyond lighter fluid?

There are a number of alternatives, just depends on how much you want to pay. Bright light behind the stamp sometimes works. Watermark Fluid works fine but is quite expensive. I use the brand Clarity.

You might be surprised how good a scan against a black background works, especially with used stamps. Some stamps, like some German ones, remain tricky.

Water works very well and is non-toxic, too. BUT you cannot use it on stamps with gum and you also need to avoid using it with stamps printed with water-soluble ink.

I have used lighter fluid for 60 years with no problems. Used watermark fluid for a few years but when it went above $10.00 a bottle I went back to lighter fluid (about $2.50 at Walmart).
I also use the lighter fluid/ baby powder method to soak self-adhesive stamps. works great.

I have used Lghter fluid, mark one eyeball on a black background and bright back light. it is unusual for a watermark to be visible to the naked eye, but sometimes it is. currently I use an anhydrous alcohol as used in a biomedical laborotory. A Phd student gave me some in 2019 when the 200 ml is all used up I will revert to Lighter fluid. the brands I use in the UK all have a Light Aliphatic listed as an ingredient.some state the aliphatic is something like 0.1%. My scientific friend confirmed this is a grease, but it was an absolutely minute amount. I have used the "proper" watermark detector fluid but found it was so volatile I scarcely had time to look for the watermark before it evaporated. As I understand it our local brick and mortar stamp shop use lighter fluid as one method of viewing watermarks. There is some kind of light which you can use to detect watermarks. A freind uses one as it is less messy, but says he thinks it is no more successful then watermark fluid. IE it usually works.