To make it look like tartan the trick is to use two main colours that produce another shade where the lines meet. For my blanket I chose magenta and teal with purple cross over squares on a neutral grey background.
Stylecraft Special DK 100g
4 x silver
2 x magenta
2 x petrol
1 x emperor
4mm crochet hook.
Finished blanket was 14 x 14 squares and measured approximately 110cm (43") square. It's easy to make a larger blanket by repeating the pattern.
I made basic crochet granny squares, working three rounds before fastning off. I followed the pattern below and joined the squares together as I went along but if you're joining them later you need to make the following number of squares in each colour:
100 x silver
40 x magenta
40 x petrol
16 x emperor
My granny square pattern (UK crochet terms)
Make 5 chains and join in a circle with a slip stitch.
Round 1: Make 3ch to count as first treble, into the circle work 2tr, 2ch. (3tr, 2ch) three times. Join with a slip stitch to the top of the first 3ch.
Rounds 2: Slip stitch into the next 2tr and 2ch loop. Make 3ch, 2tr, 2ch 3tr into the 2ch loop, 1ch. *3tr, 2 ch, 3tr into the next 2ch loop, 1ch. Repeat from * two more times. Join with a slip stitch to the top of the first 3ch.
Round 3: Slip stitch into the next 2tr and 2ch loop. Make 3ch, 2tr, 2ch, 3tr into the 2ch loop, 1ch. *3tr in the next 1ch space, 1ch. (3tr, 2 ch, 3tr) into the next 2ch loop, 1ch. Repeat from * twice more. 3tr in the next 1ch space, 1ch. Join with a slip stitch to the top of the first 3ch and fasten off.
Join the squares in the following pattern.
S - silver (grey)
M - magenta (pink)
P - petrol (blue)
E - emperor (purple)
I finished the blanket off with three rounds of double chains (US single chains) in emperor to give it a neat edge. I worked 3dc into each corner, one dc into the top of each tr, 1dc into each 1ch space and 2dc together where the squares join (1dc into each corner 2ch space, worked together).
The pattern is adaptable to any number of colour combinations but I think it looks best if you stick to colours that blend to form another colour, for example yellow and red crossing over to make orange, or blue and yellow crossing over to make green.
You can make the blanket any size you like by simply working as many pattern repeats as required. Each square measures approximately 7cm (3")