My first time shooting long exposure seascapes on film with a Mamiya RB67 and a 10 stop ND filter

My first time shooting long exposure on film.
I loaded my trusty Mamiya RB67 with Ilford HP5 and a bought along a cheap 10 stop ND filter that I bought on eBay.

Before embarking on this I did a bit of research and discovered something I had never heard of before, Reciprocity Failure.
Basically, film sensitivity diminishes over time, so the normal (ie. shooting with a digital camera) rules of measuring exposure don't apply.
I found a table for HP5 online and was surprised how much longer my timings needed to be.

So, referencing between a light meter, the Lee Filters Big Stopper ND exposure app and the Reciprocity Failure table takes some getting use to, but everything seemed to work out fine... apart from the first shot where I forgot to attach the ND filter!

I developed the film at home with a Lab-Box and some Cinestill Monobath and I have to say, I was pleasantly surprised by the results.

Any tips on shooting long exposures on film greatly appreciated.

http://www.adjbrown.com/