When decreasing one of my favorites is just SSK followed by K2Tog. By using them in this order, and without any center stitches, you do not get a strongly visible seam, all you notice is that the stitches change direction along the decrease line.
Now I would want to match this with increases without getting any holes. The closest I have gotten is by doing RLI, K1 twisted, LLI. I twist in alternating direction the center stitch to make it less dominating.
Do you have any other suggestion for a hole free double increase without a center line, or if there is a center line it should hardly be visible?
Without the twist you will have a column with V between the increases and it would not match the decrease (SSK, K2Tog). Without the twist it would instead match centered double decrease, which is also having a V column in the middle. Now I want the increase and decrease as invisible as possible, thus no extra decorating V columns.
Whenever you stack your increases or decreases (having them right above the last one), you will have a “line” start to be created. Sometimes we want that line, such as in raglan sleeves, or the centre spine of a triangular shawl, but sometimes not. If you don’t want a line created, try moving that increase/decrease a little before or after the last one, if it is possible. When you stagger the increases/decreases, they are less noticeable.