If you're hiring for an Art Director position that means there will be other designers who will be managed by this employee. The Art Director rarely does the technical work but still needs to know about the process and how to get the most out of his team.
Even if the Senior Designer will not work in the same workplace, he
will still need to work in collaboration with your team. It's in fact
even worse if that person isn't at the same workplace; you need to
make sure the designer has a strong discipline, lot of initiative, problem solving skills and can clearly
communicate with limited options (eg. Skype, phone, emails.)
So the questions you should ask should include a lot of questions about team, project, and conflict resolution. There's great designers who are seniors but will totally destroy the unity of a team because of their ego, lack of social skills, bad communication, lack of team management experience, etc.
Time management and a team work attitude is what you'll need for that
kind of position; this way this new employee will fix things and get
them done, instead of creating more issues that the bosses will need
to waste time on.
The best questions for this (or at least include some of them in your interview) are the one with problematic situations scenario. A good team leader and Art Director can suck at design but can still get the best results because... he/she listens to his/her team and knows how to use the strength of the other designers or coders.
His/her personal style preferences don't matter much as long he/she can understand the business psychology and what clients' want... You also need to find questions that will show if the Art Director has a solid personality and can resist pressure, bullying and can be assertive without being disrespectful. You want to find someone who has a great emotional intelligence; it's even more important than being technically good at design. It's very expensive to train new employees and find good ones as well; you don't want to waste time hiring someone with a huge ego who will make your other good employees/co-workers demoralized.
It's way easier to learn graphic skills and techniques than learning
how to be emotionally / time / business smart! A designer well balanced in these areas will find ways to improve their design and layouts, and will not have issues using the right resources or ask for honest feedback to improve their work.
You might not like 100% of the portfolio of the Senior Designer but as someone else pointed out, you don't know what were the challenges with these designs and they should also be seen in their context (e.g. when they were done.) Maybe one thing you can do is asked about random projects in the portfolio and ask the designer why he decided this was a good piece to present and why.
Examples of questions:
- What do you think the fundamental purpose of a manager is? (You’re
looking for someone who knows it’s about getting things done, not
something touchy-feely.)
- What do you think are some of the most common ways people fail at
management?
- How do you handle a project that has limited resources in time, money
and feedback? How do you know you did a good job and can show the result to the client?
- How would the people around you describe you? (You don't want someone who has an "open-door" policy because that shows lack of time management skills, or "I'm friend with everybody" which might be a sign of not being assertive. Usually assertive managers are not loved by every single employees...!)
- What’s a common misconception some people have about you?
- Tell me about a difficult decision you had to make recently with a project. Walk me
through the problem and what your thought process was, and how you
ultimately handled it.
- What’s an example of a goal you didn’t meet? How come? How did you
respond to that?
- Tell me about one of the organization’s largest or most important
projects and how you managed it, from start to finish. I’m interested
in something where others were doing the work, but you were
overseeing it. - What was the vision for it? - What happened? - How
did you ensure that happened?
- Tell me about something you got done at ___ that someone else in your
role probably wouldn’t have.
- Tell me about the most difficult employee/project situation you ever
had to handle. What did you do and what was the result?
- Have you ever been given criticism that you disagreed with? What was
it? How did you handle that?
- What do you do when a client/co-worker gives you very harsh criticisms that you
judge unfair or think are technically wrong? (You want to know if the Senior
Designer will fight his way with the client and can support
criticism, and also if he/she also has good business relationship
aptitudes. You don't want someone who will fight the client or other employees.)
- What are your goals when you plan or prepare a project?
- How do you deal with co-workers who are passive-aggressive, or don't
want to do what you suggested? How do you manage the situation?
- What do you do when you need feedback, details or material to
complete your project but the people who should give them to you are
late? What if you cannot get these information or this material?
- etc.
Most of the questions come from: http://managerlink.monster.com/training-personnel/articles/328-interview-questions-to-ask-when-hiring-a-manager