Why draw design lines on the Block? Why not keep the block nice and clean. Why not trace the block and draw the design lines on the paper pattern?
Maybe experienced patternmakers work this way, and you can choose to as well, but there are a few reasons you may want to mark lines on the block, especially when you are new to patternmaking.
Saves Work (the next time around)
This is relevant in cases such as:
- Empire Line Markings (see Image 1 below)
- Contour Markings (see Image 2 below)
You work it out once, the information is on the block, and you have that information to use again next time you make an style with an Empire Line, or next time your garment needs contouring (which will be often). If you did not put this information on the block, but just traced the block and put that information on the pattern you are making, next time you went to create an Empire Line garment (or do contouring), you'd have to do all the work again. Or you'd have to look it up on notes you have written down somewhere. (If you are a very experienced patternmaker after time you will probably just remember all that information without having to refer to notes).
Saves Work (this time around)
So you may understand why information that is used again and again is put on the block, but why general design lines? In the image below (Image 3), why not just trace the block and draw the Princess Line on the paper pattern?
If you just copy the block onto paper (as in Image 3, the pattern pieces on the right hand side), you will then need to cut the paper through the design line. This means you have no paper for seam allowance at the cutting line... You will need to put paper underneath, stick the two pattern pieces onto that paper. (It will also be necessary to cut up pattern piece #2 to close the side dart....).
Drawing the design line on the block, and using that information, allows you to create the two pattern pieces one at a time on the paper below, meaning you can leave room for seam allowance. You can also pivot the side seam dart into the design line at the same time.
Summary of... Why?
The bottom line is; it saves work. Either this time or next time.
Drawing lines on your block doesn't mean that you will never have to cut up the resultant pattern, put paper underneath, stick the pieces together (and maybe do it all a second or a third time), but you won't have to do it as often.
Note: Lines such as neckline depths or neckline shapes are really useful to have on a block, especially if it is a personalised block. You get to know the best neckline depths and shapes to suit your body, and it's very useful to have this information on your block.
Doesn't the Block get messy?
In Image 1, the only markings are the Empire Line markings, in Image 2, only the Contour Markings. In Image 3, only the current design line (Princess Line). But in reality a block may have all three plus more (various design lines). Doesn't this get messy? Maybe so, but it's useful to have that information on there.