Those look like carbon film resistors in the photo.
If carbon films or carbon composition resistor get heat during normal operation, they will slowly decrease in value. For this reason they have to be run at values substantially less than their ratings- no more than 20% dissipation!
If carbon films or carbon composition resistor get heat during normal operation, they will slowly decrease in value. For this reason they have to be run at values substantially less than their ratings- no more than 20% dissipation!