Best type of pen/ink for addressing invites?

I'm going to hand-address my invitations. I bought a template on for keeping the lines straight. For the people who hand addressed envelopes, what type of pen did

How to Respond to a Wedding Invitation — Emily Post

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Best type of pen/ink for addressing invites?, Weddings, Do It Yourself, Wedding Forums

Silhouette sketch pens for customized wedding invitation envelopes

Silhouette sketch pens for customized wedding invitation envelopes

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How to Address Guests on Wedding Invitation Envelopes Wedding invitation etiquette, Addressing envelopes wedding, Addressing wedding invitations