Do any of you fine folks burn packaged logs in your fireplace?

[Paper Roses]

For the past few years I have burned Duralogs and pine logs((packed from the market)
in my kitchen fireplace. I no longer burn real wood logs because I cannot close the fireplace damper off in the evening. Need to control the heat loss up the chimney. Artificial logs burn out quickly and I can close the damper.

The last year when I used the pine logs, I noticed that there is a black residue on the fire-back wall and sides of the fireplace bricks.

There is no indication on the packages about this. I wonder if burning these artificial logs leaves some kind of residue and perhaps I should forget about using them.

Has anyone else noticed this?
What do you use in place of regular wood?

My fireplaces are over 200 years old and I do not want to have real wood fires. I can not pay for a chimney cleaning and the possible necessity of repair. Miss the fires but am concerned about artificial logs.

Your experiences?
Any ideas would be a great help.
Thanks.