Well, my TIPPETTE (*) for today is to simply boil 1" of water in a cup in the microwave, then drop the tube (head first) into it, and within a minute, you'll be able to twist off that cap very nicely (do NOT boil the water with the tube in it, and use a paper towel when you grab the tube from the water!). It's likely that this will also help if your paint itself has hardened in the tube...it should come out nice and fresh.
Note: Not long ago, I bought some new tubes of paint and, within 6 months, the tube CAP on one of them actually broke off in 2, at the neck! So I emailed the manufacturer and showed them some pics (I told them I KNEW they'd want to know about it!). They immediately sent me a replacement tube! THAT's good Customer Service! And, as a follow up to this story, I had the cap break in two, from a totally different manufacturer. When I called them, they said they were sorry but there was nothing they could do. I then relayed what the other manufacturer had done, and in the end, they sent me a couple of new plastic replacement caps (I was totally ok with that). Honestly, they should know not to cross an artist who spends hard-earned money on their products, right? How often have you had trouble with YOUR caps? I can't be the only one!
(*) TIPPETTE = Snippet of a Tip (in watercolor)
In April 2013, I posted 30 Tippettes (1 per day) on my Blog. Find the 30th one HERE. When you scroll down after reading that one, you'll see Older Tippettes. When you can't scroll down any further, look at the bottom right hand side under the last post, and look for the words OLDER POST. When you click on that, you'll see the rest. Just thought you'd want to know. Do you have a favorite watercolor tip of your own? Please post them as a Comment below, or reply to my email if that's how you receive my Blog posts, and I'll post it for you. (Tips can refer to tools, techniques, habits,...anything that helps YOU might help someone else too. Let's be Sharers). Happy Painting!