Have never had a gas dryer so the following is just a general observation
As far as I know there is only 4 ways to get a black film
1. Something is rapidly wearing in the dryer and giving off black powder. Perhaps an oilite roller bearing. Very Unlikely
2. The natural gas is contaminated also unlikely but can happen
If you have a neighbor who also has a gas dryer are they having a problem or if you have a gas stove are the burners very yellow recently
3. The dryer is starving for oxygen for some reason ( air flow restriction somewhere). This is the most likely cause. It is also very dangerous due to increased production of Carbon Monoxide. Make sure the vent, blower and lint filter path are clean and operating correctly
4. Vent is not operating correctly, dryer forces lint into the dryer cabinet, burns it and ends up on your clothes. Same fix as above, also check seals at front and back of dryer drum |