I had to look these up. "Lettrism" is a 1940s French artistic movement, closely associated with an artist named Isou, and not familiar to people who are not deeply interested in art and art history. "Amplic" and "chiselling" are technical terms invented by Isou himself. They are specific to discussions of this art movement. You are not going to find much help in general language books or ordinary dictionaries. I suggest the Wikipedia article on Lettrism, and the section on "the Amplic and the Chiselling phases," as a starting point. https://en.wikipedia.org/wiki/Lettrism#The_Amplic_(amplique)_and_the_Chiselling_(ciselante)_phases "Chiselling" (spelled with two L's in the UK, and one L, "chiseling," in the US) means "to use a chisel." A chisel is a cutting tool. There's a picture here: https://tinyurl.com/y89mtqsy A chisel is used for rough shaping. A woodcarver might use a chisel first to get a rough shape into the wood quickly. He then might use other tools to smooth it. Someone with a very rugged, irregular-looking, rough face can be said to have "chiseled" features. Isou had some grand theory about the way in which any art form develops. "Amplic" and "chiseling" refer to different stages in any art form. The Wikipedia article says the amplic phase ends when the art form is fully developed and finished, and there is no more to be done. "This then inaugurated a chiselling phase in the art. Whereas the form had formerly been used as a tool to express things outside its own domain—events, feelings, etc.--it would then turn in on itself and become, perhaps only implicitly, its own subject matter." Because this sounds like pretentious nonsense to me, I can't explain it!

"only after reading the wiki link that Dan provided" I have concluded that it is a load of "codswallop" <--(old British term) the modern term would transgress Itaki's policies. I read it similar to Dan but like this. In any art form there are people and artists who set down a "standard" or "template" about what a poem, song, sculpture etc should be and people basically follow those precedents. These are called the amplic stages of art. Thereafter the only way to go for other artists is to try and make small adjustments to the templates already laid down. This process is called the chiselling stage. "so far the theory is making sense" then it goes awry and the theory tries to explain art at any stage in mans history or future history using this "template" plus "chiselling" theory. Shakespeare, and many others from many lands and many cultures would have provided a "amplic template" for others to "Chisel at" to give us our current art form. However there has to be artists in the future who provide new totally different "amplic templates" to be "chiselled at". WHO ? lay down the "amplic template" for the Statues on "the Easter Islands" and the cave paintings all over the globe. It's a nonsensical theory to say what many languages can say in one sentence. "ART EVOLVES"