One of my favorite discussions and explanations of casing layers, by Paul Stamets and J.S. Chilton

Q: “can you explain how you mist once you see your first pins? thanks!” A:  Greetings mycopal!Allow me to provide you with some additional information to fully address your question :) Pinning is a process that occurs throughout the entire colonized cake, where the mycelium's metabolic processes shift towards fruiting. This is why, if someone's cake develops significant side pins, you often only see pinning there, rather than flat-surface pins through the fruiting phase. It's important to ensure that the colonizing mycelium is not exposed to the same lighting conditions as during fruiting. I personally keep black tarp material on my shelves to prevent light from hitting the bottom of the clear totes. However, light serves as a secondary trigger for pinning, while increased fresh air exchange (FAE), a drop in temperature, and the presence of condensation droplets on the mycelial mat (which later dry up) are the primary triggers for pinning after colonization is complete. In my current setup using unmodified and modified 6qt shoebox tubs, I don't need to mist much. During colonization, I don't mist at all. The lid on the 6qt tubs, combined with the substrate's field capacity, provides enough moisture. You should notice notable condensation on all walls of the tubs throughout the entire process. The shoeboxes have built-in gaps in the lid-lock structure that allow for some passive FAE. These tubs were originally designed to allow air circulation for storing shoes (particularly for shoe collectors), but the passive FAE is sufficient to let excessive carbon dioxide escape while maintaining humidity around 90%. When I observe full colonization of the subsurface sides of the tub and at least 80% of the tub surface covered in surface mycelium, I transition to the fruiting stage. My process has become quite straightforward: I remove the lid from the colonized tub and place a new shoebox tub (which may or may not be modified) upside down on top of it. Before placing the new tub, I mist it lightly. Then, I move the tub to a lower shelf in my grow and research area. The top level shelves are not exposed to my grow lights and are slightly shaded; and has a slightly lower ambient temperature. I also have a timed HEPA filter running on the lowest setting, cycling on and off every 6 hours. Additionally, I use brand: mostthink LED plant lights on the fruiting shelves. This tub setup allows light to spread evenly over the substrate surface, through the new-tub into the colonized tub more effectively compared to fruiting with the lid on. If you choose to fruit with the lid on, you need to be mindful of the direction from which the light enters as the fruits can grow sideways. At this point, I still haven't misted the colonized substrate or the inner walls of the tub. The lips of the two shoebox tubs should align, but there can be a slight offset, which helps with passive FAE and allows intentional air-filtered flow for exchanging fresh air and removing carbon dioxide. After a few days, I usually start to observe budding primordia as the increased FAE and air exchange in the tub cause the condensation on the mycelial mat to dry up. Once you see primordia, it becomes easy to spot their development from that point onwards. At this stage, I closely monitor the humidity in the tub. If I notice a lack of present and collecting condensation droplets on the inner walls of both the colonized and "roof" tub, I may use a light misting hand-pump spray bottle. I personally use a 250mL hair stylist mister bottle with filtered (or boiled and cooled) water, to which I add 1 tsp of H202. However, I never spray the mycelium or the fruits directly. I MAY do a misted spray upwards, away from the colonized tub, and let it slowly sway and sink onto the substrate (but only if I havent begun to see primordia forming in that few day window I discussed above). I do this, primarily because of my belief/understanding that pins form on parts of the mycelial matte (generally rhizoid growth that have laid flat) and do so in spots where there was condensation pooled that dries from the FAE increasing :) Does this help? Follow up questions? :)Thanks for reading!