Changing yarn weight

Hello!

I’d like to crochet a double-layered blanket, but instead of simply crocheting two finished blankets together, I want to work the whole thing in one go.
It should look like this: The front has color gradient 1, and the back has color gradient 2. The two colored sides are interrupted at regular intervals by a black row that connects the front and back.

I thought that if I work a black row like this and combine the front and back, then the black yarn needs to be thicker, because otherwise these rows would be much thinner than the rest of the blanket. That would mean using hook size 4 for the two sides and hook size 6 for the black stripes.

But now I’ve realized that this will make the black rows not only thicker but also WIDER. So I have to balance that out somehow.

- Should I work fewer stitches in the black row, that is, decrease regularly so the width is right? (And if so, by what ratio?) Then I’d have to increase again right away on the colored sides. That sounds like a hassle.

- Should I, regardless of the yarn weight, work the whole piece only with size 4 or only with size 6? Then one would be veeeery loose, or the other veeeery stiff and maybe still wider.

- Should I just crochet through with the same number of stitches and the different hook sizes, risking a wavy edge or maybe even overall puckering? Or would that actually look appealing? 

I’d be incredibly grateful if someone here has tried something like this before and would be willing to help me out.
I could make a small gauge swatch, but I’m afraid it wouldn’t show what the effect would be if I started with 300 stitches over a 1.50-meter width.

Thanks in advance!

You could use a gauge swatch to figure out how much wider the blanket would become. Then, in the thick row, decrease every second, third, or xth stitch, and increase again in the thin row by working every second, third, or xth stitch twice.
That would involve a bit of counting, but nothing more than that.

How many rows do you have to knit in black? Maybe that’s something else to keep in mind. 

The blanket is being crocheted.

I was thinking of crocheting about 7–10 rows of the double-layered color gradients using 4 strands with hook size 3.5, and then inserting just one row of double crochets using 8 strands with hook size 6 in between. 

You’ve given me an idea!
On the thick row, I could work only in every other stitch—two double crochets, worked together, with a chain stitch in between. That way, the number of stitches doesn’t change, but the gaps allow these thicker stitches to expand freely without forcing the whole piece to widen. I’ll give that a try.

Thanks!

Maybe you could let us know whether it works and show us a picture 

Good luck and have a lovely Easter weekend 

I’ll do that!