The basic repertoire of pattern welded steel starts with a layered bar of more or less parallel sheets of at least two varieties of steel. This bar can be manipulated by several basic operations to achieve a nice stable of patterns without killing one's self on mosaic or a lot of real expensive equipment. The most familiar deliberate patterns are ladder and twist. To make a ladder pattern, the layered bar is either cut into at regular intervals across the width of the bar, then forged out flat again, or alternatively, the bar can be forged into a die set to raise bumps across the width of the bar, and then the resultant bumps or ridges ground off afterward. They appear very similar in the end, and I do not think one or the other is better or worse, personally.
Twist pattern is sort of self-explanatory.
The bar is made to be square to round in section, then heated and twisted, then forged flat again. I normally forge the bar to an octagonal section, not square, and not exactly round either, if I am going to do a simple single bar twist. Do the twisting at welding heat, or nearly so to minimize the chances of the bar coming from together to apart. Twisting put a huge amount of stress on all of the forge welds, and if they are not good, you will find out rapidly when you apply roatational torque to the bar. If a twisting apparatus is not available to you, then I suggest having an assistant if possible.