To find out how many masks can be made with 10 feet of string, we need to divide the total amount of string by the amount of string needed for each mask.
Each mask requires \( \frac{1}{2} \) foot of string.
Now, we divide the total string (10 feet) by the string needed for each mask:
\[ \text{Number of masks} = \frac{10 \text{ feet}}{\frac{1}{2} \text{ foot per mask}} \]
To divide by a fraction, we can multiply by the reciprocal:
\[ \text{Number of masks} = 10 \times \frac{2}{1} = 10 \times 2 = 20 \]
Thus, the students in the art club can make \( \boxed{20} \) masks.